5224 lines
162 KiB
C
5224 lines
162 KiB
C
/*-------------------------------------------------------------------------
|
|
*
|
|
* procarray.c
|
|
* POSTGRES process array code.
|
|
*
|
|
*
|
|
* This module maintains arrays of PGPROC substructures, as well as associated
|
|
* arrays in ProcGlobal, for all active backends. Although there are several
|
|
* uses for this, the principal one is as a means of determining the set of
|
|
* currently running transactions.
|
|
*
|
|
* Because of various subtle race conditions it is critical that a backend
|
|
* hold the correct locks while setting or clearing its xid (in
|
|
* ProcGlobal->xids[]/MyProc->xid). See notes in
|
|
* src/backend/access/transam/README.
|
|
*
|
|
* The process arrays now also include structures representing prepared
|
|
* transactions. The xid and subxids fields of these are valid, as are the
|
|
* myProcLocks lists. They can be distinguished from regular backend PGPROCs
|
|
* at need by checking for pid == 0.
|
|
*
|
|
* During hot standby, we also keep a list of XIDs representing transactions
|
|
* that are known to be running on the primary (or more precisely, were running
|
|
* as of the current point in the WAL stream). This list is kept in the
|
|
* KnownAssignedXids array, and is updated by watching the sequence of
|
|
* arriving XIDs. This is necessary because if we leave those XIDs out of
|
|
* snapshots taken for standby queries, then they will appear to be already
|
|
* complete, leading to MVCC failures. Note that in hot standby, the PGPROC
|
|
* array represents standby processes, which by definition are not running
|
|
* transactions that have XIDs.
|
|
*
|
|
* It is perhaps possible for a backend on the primary to terminate without
|
|
* writing an abort record for its transaction. While that shouldn't really
|
|
* happen, it would tie up KnownAssignedXids indefinitely, so we protect
|
|
* ourselves by pruning the array when a valid list of running XIDs arrives.
|
|
*
|
|
* Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
|
|
* Portions Copyright (c) 1994, Regents of the University of California
|
|
*
|
|
*
|
|
* IDENTIFICATION
|
|
* src/backend/storage/ipc/procarray.c
|
|
*
|
|
*-------------------------------------------------------------------------
|
|
*/
|
|
#include "postgres.h"
|
|
|
|
#include <signal.h>
|
|
|
|
#include "access/clog.h"
|
|
#include "access/subtrans.h"
|
|
#include "access/transam.h"
|
|
#include "access/twophase.h"
|
|
#include "access/xact.h"
|
|
#include "access/xlogutils.h"
|
|
#include "catalog/catalog.h"
|
|
#include "catalog/pg_authid.h"
|
|
#include "commands/dbcommands.h"
|
|
#include "miscadmin.h"
|
|
#include "pgstat.h"
|
|
#include "port/pg_lfind.h"
|
|
#include "storage/proc.h"
|
|
#include "storage/procarray.h"
|
|
#include "storage/spin.h"
|
|
#include "utils/acl.h"
|
|
#include "utils/builtins.h"
|
|
#include "utils/rel.h"
|
|
#include "utils/snapmgr.h"
|
|
|
|
#define UINT32_ACCESS_ONCE(var) ((uint32)(*((volatile uint32 *)&(var))))
|
|
|
|
/* Our shared memory area */
|
|
typedef struct ProcArrayStruct
|
|
{
|
|
int numProcs; /* number of valid procs entries */
|
|
int maxProcs; /* allocated size of procs array */
|
|
|
|
/*
|
|
* Known assigned XIDs handling
|
|
*/
|
|
int maxKnownAssignedXids; /* allocated size of array */
|
|
int numKnownAssignedXids; /* current # of valid entries */
|
|
int tailKnownAssignedXids; /* index of oldest valid element */
|
|
int headKnownAssignedXids; /* index of newest element, + 1 */
|
|
slock_t known_assigned_xids_lck; /* protects head/tail pointers */
|
|
|
|
/*
|
|
* Highest subxid that has been removed from KnownAssignedXids array to
|
|
* prevent overflow; or InvalidTransactionId if none. We track this for
|
|
* similar reasons to tracking overflowing cached subxids in PGPROC
|
|
* entries. Must hold exclusive ProcArrayLock to change this, and shared
|
|
* lock to read it.
|
|
*/
|
|
TransactionId lastOverflowedXid;
|
|
|
|
/* oldest xmin of any replication slot */
|
|
TransactionId replication_slot_xmin;
|
|
/* oldest catalog xmin of any replication slot */
|
|
TransactionId replication_slot_catalog_xmin;
|
|
|
|
/* indexes into allProcs[], has PROCARRAY_MAXPROCS entries */
|
|
int pgprocnos[FLEXIBLE_ARRAY_MEMBER];
|
|
} ProcArrayStruct;
|
|
|
|
/*
|
|
* State for the GlobalVisTest* family of functions. Those functions can
|
|
* e.g. be used to decide if a deleted row can be removed without violating
|
|
* MVCC semantics: If the deleted row's xmax is not considered to be running
|
|
* by anyone, the row can be removed.
|
|
*
|
|
* To avoid slowing down GetSnapshotData(), we don't calculate a precise
|
|
* cutoff XID while building a snapshot (looking at the frequently changing
|
|
* xmins scales badly). Instead we compute two boundaries while building the
|
|
* snapshot:
|
|
*
|
|
* 1) definitely_needed, indicating that rows deleted by XIDs >=
|
|
* definitely_needed are definitely still visible.
|
|
*
|
|
* 2) maybe_needed, indicating that rows deleted by XIDs < maybe_needed can
|
|
* definitely be removed
|
|
*
|
|
* When testing an XID that falls in between the two (i.e. XID >= maybe_needed
|
|
* && XID < definitely_needed), the boundaries can be recomputed (using
|
|
* ComputeXidHorizons()) to get a more accurate answer. This is cheaper than
|
|
* maintaining an accurate value all the time.
|
|
*
|
|
* As it is not cheap to compute accurate boundaries, we limit the number of
|
|
* times that happens in short succession. See GlobalVisTestShouldUpdate().
|
|
*
|
|
*
|
|
* There are three backend lifetime instances of this struct, optimized for
|
|
* different types of relations. As e.g. a normal user defined table in one
|
|
* database is inaccessible to backends connected to another database, a test
|
|
* specific to a relation can be more aggressive than a test for a shared
|
|
* relation. Currently we track four different states:
|
|
*
|
|
* 1) GlobalVisSharedRels, which only considers an XID's
|
|
* effects visible-to-everyone if neither snapshots in any database, nor a
|
|
* replication slot's xmin, nor a replication slot's catalog_xmin might
|
|
* still consider XID as running.
|
|
*
|
|
* 2) GlobalVisCatalogRels, which only considers an XID's
|
|
* effects visible-to-everyone if neither snapshots in the current
|
|
* database, nor a replication slot's xmin, nor a replication slot's
|
|
* catalog_xmin might still consider XID as running.
|
|
*
|
|
* I.e. the difference to GlobalVisSharedRels is that
|
|
* snapshot in other databases are ignored.
|
|
*
|
|
* 3) GlobalVisDataRels, which only considers an XID's
|
|
* effects visible-to-everyone if neither snapshots in the current
|
|
* database, nor a replication slot's xmin consider XID as running.
|
|
*
|
|
* I.e. the difference to GlobalVisCatalogRels is that
|
|
* replication slot's catalog_xmin is not taken into account.
|
|
*
|
|
* 4) GlobalVisTempRels, which only considers the current session, as temp
|
|
* tables are not visible to other sessions.
|
|
*
|
|
* GlobalVisTestFor(relation) returns the appropriate state
|
|
* for the relation.
|
|
*
|
|
* The boundaries are FullTransactionIds instead of TransactionIds to avoid
|
|
* wraparound dangers. There e.g. would otherwise exist no procarray state to
|
|
* prevent maybe_needed to become old enough after the GetSnapshotData()
|
|
* call.
|
|
*
|
|
* The typedef is in the header.
|
|
*/
|
|
struct GlobalVisState
|
|
{
|
|
/* XIDs >= are considered running by some backend */
|
|
FullTransactionId definitely_needed;
|
|
|
|
/* XIDs < are not considered to be running by any backend */
|
|
FullTransactionId maybe_needed;
|
|
};
|
|
|
|
/*
|
|
* Result of ComputeXidHorizons().
|
|
*/
|
|
typedef struct ComputeXidHorizonsResult
|
|
{
|
|
/*
|
|
* The value of ShmemVariableCache->latestCompletedXid when
|
|
* ComputeXidHorizons() held ProcArrayLock.
|
|
*/
|
|
FullTransactionId latest_completed;
|
|
|
|
/*
|
|
* The same for procArray->replication_slot_xmin and.
|
|
* procArray->replication_slot_catalog_xmin.
|
|
*/
|
|
TransactionId slot_xmin;
|
|
TransactionId slot_catalog_xmin;
|
|
|
|
/*
|
|
* Oldest xid that any backend might still consider running. This needs to
|
|
* include processes running VACUUM, in contrast to the normal visibility
|
|
* cutoffs, as vacuum needs to be able to perform pg_subtrans lookups when
|
|
* determining visibility, but doesn't care about rows above its xmin to
|
|
* be removed.
|
|
*
|
|
* This likely should only be needed to determine whether pg_subtrans can
|
|
* be truncated. It currently includes the effects of replication slots,
|
|
* for historical reasons. But that could likely be changed.
|
|
*/
|
|
TransactionId oldest_considered_running;
|
|
|
|
/*
|
|
* Oldest xid for which deleted tuples need to be retained in shared
|
|
* tables.
|
|
*
|
|
* This includes the effects of replication slots. If that's not desired,
|
|
* look at shared_oldest_nonremovable_raw;
|
|
*/
|
|
TransactionId shared_oldest_nonremovable;
|
|
|
|
/*
|
|
* Oldest xid that may be necessary to retain in shared tables. This is
|
|
* the same as shared_oldest_nonremovable, except that is not affected by
|
|
* replication slot's catalog_xmin.
|
|
*
|
|
* This is mainly useful to be able to send the catalog_xmin to upstream
|
|
* streaming replication servers via hot_standby_feedback, so they can
|
|
* apply the limit only when accessing catalog tables.
|
|
*/
|
|
TransactionId shared_oldest_nonremovable_raw;
|
|
|
|
/*
|
|
* Oldest xid for which deleted tuples need to be retained in non-shared
|
|
* catalog tables.
|
|
*/
|
|
TransactionId catalog_oldest_nonremovable;
|
|
|
|
/*
|
|
* Oldest xid for which deleted tuples need to be retained in normal user
|
|
* defined tables.
|
|
*/
|
|
TransactionId data_oldest_nonremovable;
|
|
|
|
/*
|
|
* Oldest xid for which deleted tuples need to be retained in this
|
|
* session's temporary tables.
|
|
*/
|
|
TransactionId temp_oldest_nonremovable;
|
|
} ComputeXidHorizonsResult;
|
|
|
|
/*
|
|
* Return value for GlobalVisHorizonKindForRel().
|
|
*/
|
|
typedef enum GlobalVisHorizonKind
|
|
{
|
|
VISHORIZON_SHARED,
|
|
VISHORIZON_CATALOG,
|
|
VISHORIZON_DATA,
|
|
VISHORIZON_TEMP
|
|
} GlobalVisHorizonKind;
|
|
|
|
/*
|
|
* Reason codes for KnownAssignedXidsCompress().
|
|
*/
|
|
typedef enum KAXCompressReason
|
|
{
|
|
KAX_NO_SPACE, /* need to free up space at array end */
|
|
KAX_PRUNE, /* we just pruned old entries */
|
|
KAX_TRANSACTION_END, /* we just committed/removed some XIDs */
|
|
KAX_STARTUP_PROCESS_IDLE /* startup process is about to sleep */
|
|
} KAXCompressReason;
|
|
|
|
|
|
static ProcArrayStruct *procArray;
|
|
|
|
static PGPROC *allProcs;
|
|
|
|
/*
|
|
* Cache to reduce overhead of repeated calls to TransactionIdIsInProgress()
|
|
*/
|
|
static TransactionId cachedXidIsNotInProgress = InvalidTransactionId;
|
|
|
|
/*
|
|
* Bookkeeping for tracking emulated transactions in recovery
|
|
*/
|
|
static TransactionId *KnownAssignedXids;
|
|
static bool *KnownAssignedXidsValid;
|
|
static TransactionId latestObservedXid = InvalidTransactionId;
|
|
|
|
/*
|
|
* If we're in STANDBY_SNAPSHOT_PENDING state, standbySnapshotPendingXmin is
|
|
* the highest xid that might still be running that we don't have in
|
|
* KnownAssignedXids.
|
|
*/
|
|
static TransactionId standbySnapshotPendingXmin;
|
|
|
|
/*
|
|
* State for visibility checks on different types of relations. See struct
|
|
* GlobalVisState for details. As shared, catalog, normal and temporary
|
|
* relations can have different horizons, one such state exists for each.
|
|
*/
|
|
static GlobalVisState GlobalVisSharedRels;
|
|
static GlobalVisState GlobalVisCatalogRels;
|
|
static GlobalVisState GlobalVisDataRels;
|
|
static GlobalVisState GlobalVisTempRels;
|
|
|
|
/*
|
|
* This backend's RecentXmin at the last time the accurate xmin horizon was
|
|
* recomputed, or InvalidTransactionId if it has not. Used to limit how many
|
|
* times accurate horizons are recomputed. See GlobalVisTestShouldUpdate().
|
|
*/
|
|
static TransactionId ComputeXidHorizonsResultLastXmin;
|
|
|
|
#ifdef XIDCACHE_DEBUG
|
|
|
|
/* counters for XidCache measurement */
|
|
static long xc_by_recent_xmin = 0;
|
|
static long xc_by_known_xact = 0;
|
|
static long xc_by_my_xact = 0;
|
|
static long xc_by_latest_xid = 0;
|
|
static long xc_by_main_xid = 0;
|
|
static long xc_by_child_xid = 0;
|
|
static long xc_by_known_assigned = 0;
|
|
static long xc_no_overflow = 0;
|
|
static long xc_slow_answer = 0;
|
|
|
|
#define xc_by_recent_xmin_inc() (xc_by_recent_xmin++)
|
|
#define xc_by_known_xact_inc() (xc_by_known_xact++)
|
|
#define xc_by_my_xact_inc() (xc_by_my_xact++)
|
|
#define xc_by_latest_xid_inc() (xc_by_latest_xid++)
|
|
#define xc_by_main_xid_inc() (xc_by_main_xid++)
|
|
#define xc_by_child_xid_inc() (xc_by_child_xid++)
|
|
#define xc_by_known_assigned_inc() (xc_by_known_assigned++)
|
|
#define xc_no_overflow_inc() (xc_no_overflow++)
|
|
#define xc_slow_answer_inc() (xc_slow_answer++)
|
|
|
|
static void DisplayXidCache(void);
|
|
#else /* !XIDCACHE_DEBUG */
|
|
|
|
#define xc_by_recent_xmin_inc() ((void) 0)
|
|
#define xc_by_known_xact_inc() ((void) 0)
|
|
#define xc_by_my_xact_inc() ((void) 0)
|
|
#define xc_by_latest_xid_inc() ((void) 0)
|
|
#define xc_by_main_xid_inc() ((void) 0)
|
|
#define xc_by_child_xid_inc() ((void) 0)
|
|
#define xc_by_known_assigned_inc() ((void) 0)
|
|
#define xc_no_overflow_inc() ((void) 0)
|
|
#define xc_slow_answer_inc() ((void) 0)
|
|
#endif /* XIDCACHE_DEBUG */
|
|
|
|
/* Primitives for KnownAssignedXids array handling for standby */
|
|
static void KnownAssignedXidsCompress(KAXCompressReason reason, bool haveLock);
|
|
static void KnownAssignedXidsAdd(TransactionId from_xid, TransactionId to_xid,
|
|
bool exclusive_lock);
|
|
static bool KnownAssignedXidsSearch(TransactionId xid, bool remove);
|
|
static bool KnownAssignedXidExists(TransactionId xid);
|
|
static void KnownAssignedXidsRemove(TransactionId xid);
|
|
static void KnownAssignedXidsRemoveTree(TransactionId xid, int nsubxids,
|
|
TransactionId *subxids);
|
|
static void KnownAssignedXidsRemovePreceding(TransactionId removeXid);
|
|
static int KnownAssignedXidsGet(TransactionId *xarray, TransactionId xmax);
|
|
static int KnownAssignedXidsGetAndSetXmin(TransactionId *xarray,
|
|
TransactionId *xmin,
|
|
TransactionId xmax);
|
|
static TransactionId KnownAssignedXidsGetOldestXmin(void);
|
|
static void KnownAssignedXidsDisplay(int trace_level);
|
|
static void KnownAssignedXidsReset(void);
|
|
static inline void ProcArrayEndTransactionInternal(PGPROC *proc, TransactionId latestXid);
|
|
static void ProcArrayGroupClearXid(PGPROC *proc, TransactionId latestXid);
|
|
static void MaintainLatestCompletedXid(TransactionId latestXid);
|
|
static void MaintainLatestCompletedXidRecovery(TransactionId latestXid);
|
|
|
|
static inline FullTransactionId FullXidRelativeTo(FullTransactionId rel,
|
|
TransactionId xid);
|
|
static void GlobalVisUpdateApply(ComputeXidHorizonsResult *horizons);
|
|
|
|
/*
|
|
* Report shared-memory space needed by CreateSharedProcArray.
|
|
*/
|
|
Size
|
|
ProcArrayShmemSize(void)
|
|
{
|
|
Size size;
|
|
|
|
/* Size of the ProcArray structure itself */
|
|
#define PROCARRAY_MAXPROCS (MaxBackends + max_prepared_xacts)
|
|
|
|
size = offsetof(ProcArrayStruct, pgprocnos);
|
|
size = add_size(size, mul_size(sizeof(int), PROCARRAY_MAXPROCS));
|
|
|
|
/*
|
|
* During Hot Standby processing we have a data structure called
|
|
* KnownAssignedXids, created in shared memory. Local data structures are
|
|
* also created in various backends during GetSnapshotData(),
|
|
* TransactionIdIsInProgress() and GetRunningTransactionData(). All of the
|
|
* main structures created in those functions must be identically sized,
|
|
* since we may at times copy the whole of the data structures around. We
|
|
* refer to this size as TOTAL_MAX_CACHED_SUBXIDS.
|
|
*
|
|
* Ideally we'd only create this structure if we were actually doing hot
|
|
* standby in the current run, but we don't know that yet at the time
|
|
* shared memory is being set up.
|
|
*/
|
|
#define TOTAL_MAX_CACHED_SUBXIDS \
|
|
((PGPROC_MAX_CACHED_SUBXIDS + 1) * PROCARRAY_MAXPROCS)
|
|
|
|
if (EnableHotStandby)
|
|
{
|
|
size = add_size(size,
|
|
mul_size(sizeof(TransactionId),
|
|
TOTAL_MAX_CACHED_SUBXIDS));
|
|
size = add_size(size,
|
|
mul_size(sizeof(bool), TOTAL_MAX_CACHED_SUBXIDS));
|
|
}
|
|
|
|
return size;
|
|
}
|
|
|
|
/*
|
|
* Initialize the shared PGPROC array during postmaster startup.
|
|
*/
|
|
void
|
|
CreateSharedProcArray(void)
|
|
{
|
|
bool found;
|
|
|
|
/* Create or attach to the ProcArray shared structure */
|
|
procArray = (ProcArrayStruct *)
|
|
ShmemInitStruct("Proc Array",
|
|
add_size(offsetof(ProcArrayStruct, pgprocnos),
|
|
mul_size(sizeof(int),
|
|
PROCARRAY_MAXPROCS)),
|
|
&found);
|
|
|
|
if (!found)
|
|
{
|
|
/*
|
|
* We're the first - initialize.
|
|
*/
|
|
procArray->numProcs = 0;
|
|
procArray->maxProcs = PROCARRAY_MAXPROCS;
|
|
procArray->maxKnownAssignedXids = TOTAL_MAX_CACHED_SUBXIDS;
|
|
procArray->numKnownAssignedXids = 0;
|
|
procArray->tailKnownAssignedXids = 0;
|
|
procArray->headKnownAssignedXids = 0;
|
|
SpinLockInit(&procArray->known_assigned_xids_lck);
|
|
procArray->lastOverflowedXid = InvalidTransactionId;
|
|
procArray->replication_slot_xmin = InvalidTransactionId;
|
|
procArray->replication_slot_catalog_xmin = InvalidTransactionId;
|
|
ShmemVariableCache->xactCompletionCount = 1;
|
|
}
|
|
|
|
allProcs = ProcGlobal->allProcs;
|
|
|
|
/* Create or attach to the KnownAssignedXids arrays too, if needed */
|
|
if (EnableHotStandby)
|
|
{
|
|
KnownAssignedXids = (TransactionId *)
|
|
ShmemInitStruct("KnownAssignedXids",
|
|
mul_size(sizeof(TransactionId),
|
|
TOTAL_MAX_CACHED_SUBXIDS),
|
|
&found);
|
|
KnownAssignedXidsValid = (bool *)
|
|
ShmemInitStruct("KnownAssignedXidsValid",
|
|
mul_size(sizeof(bool), TOTAL_MAX_CACHED_SUBXIDS),
|
|
&found);
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Add the specified PGPROC to the shared array.
|
|
*/
|
|
void
|
|
ProcArrayAdd(PGPROC *proc)
|
|
{
|
|
ProcArrayStruct *arrayP = procArray;
|
|
int index;
|
|
int movecount;
|
|
|
|
/* See ProcGlobal comment explaining why both locks are held */
|
|
LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
|
|
LWLockAcquire(XidGenLock, LW_EXCLUSIVE);
|
|
|
|
if (arrayP->numProcs >= arrayP->maxProcs)
|
|
{
|
|
/*
|
|
* Oops, no room. (This really shouldn't happen, since there is a
|
|
* fixed supply of PGPROC structs too, and so we should have failed
|
|
* earlier.)
|
|
*/
|
|
ereport(FATAL,
|
|
(errcode(ERRCODE_TOO_MANY_CONNECTIONS),
|
|
errmsg("sorry, too many clients already")));
|
|
}
|
|
|
|
/*
|
|
* Keep the procs array sorted by (PGPROC *) so that we can utilize
|
|
* locality of references much better. This is useful while traversing the
|
|
* ProcArray because there is an increased likelihood of finding the next
|
|
* PGPROC structure in the cache.
|
|
*
|
|
* Since the occurrence of adding/removing a proc is much lower than the
|
|
* access to the ProcArray itself, the overhead should be marginal
|
|
*/
|
|
for (index = 0; index < arrayP->numProcs; index++)
|
|
{
|
|
int procno PG_USED_FOR_ASSERTS_ONLY = arrayP->pgprocnos[index];
|
|
|
|
Assert(procno >= 0 && procno < (arrayP->maxProcs + NUM_AUXILIARY_PROCS));
|
|
Assert(allProcs[procno].pgxactoff == index);
|
|
|
|
/* If we have found our right position in the array, break */
|
|
if (arrayP->pgprocnos[index] > proc->pgprocno)
|
|
break;
|
|
}
|
|
|
|
movecount = arrayP->numProcs - index;
|
|
memmove(&arrayP->pgprocnos[index + 1],
|
|
&arrayP->pgprocnos[index],
|
|
movecount * sizeof(*arrayP->pgprocnos));
|
|
memmove(&ProcGlobal->xids[index + 1],
|
|
&ProcGlobal->xids[index],
|
|
movecount * sizeof(*ProcGlobal->xids));
|
|
memmove(&ProcGlobal->subxidStates[index + 1],
|
|
&ProcGlobal->subxidStates[index],
|
|
movecount * sizeof(*ProcGlobal->subxidStates));
|
|
memmove(&ProcGlobal->statusFlags[index + 1],
|
|
&ProcGlobal->statusFlags[index],
|
|
movecount * sizeof(*ProcGlobal->statusFlags));
|
|
|
|
arrayP->pgprocnos[index] = proc->pgprocno;
|
|
proc->pgxactoff = index;
|
|
ProcGlobal->xids[index] = proc->xid;
|
|
ProcGlobal->subxidStates[index] = proc->subxidStatus;
|
|
ProcGlobal->statusFlags[index] = proc->statusFlags;
|
|
|
|
arrayP->numProcs++;
|
|
|
|
/* adjust pgxactoff for all following PGPROCs */
|
|
index++;
|
|
for (; index < arrayP->numProcs; index++)
|
|
{
|
|
int procno = arrayP->pgprocnos[index];
|
|
|
|
Assert(procno >= 0 && procno < (arrayP->maxProcs + NUM_AUXILIARY_PROCS));
|
|
Assert(allProcs[procno].pgxactoff == index - 1);
|
|
|
|
allProcs[procno].pgxactoff = index;
|
|
}
|
|
|
|
/*
|
|
* Release in reversed acquisition order, to reduce frequency of having to
|
|
* wait for XidGenLock while holding ProcArrayLock.
|
|
*/
|
|
LWLockRelease(XidGenLock);
|
|
LWLockRelease(ProcArrayLock);
|
|
}
|
|
|
|
/*
|
|
* Remove the specified PGPROC from the shared array.
|
|
*
|
|
* When latestXid is a valid XID, we are removing a live 2PC gxact from the
|
|
* array, and thus causing it to appear as "not running" anymore. In this
|
|
* case we must advance latestCompletedXid. (This is essentially the same
|
|
* as ProcArrayEndTransaction followed by removal of the PGPROC, but we take
|
|
* the ProcArrayLock only once, and don't damage the content of the PGPROC;
|
|
* twophase.c depends on the latter.)
|
|
*/
|
|
void
|
|
ProcArrayRemove(PGPROC *proc, TransactionId latestXid)
|
|
{
|
|
ProcArrayStruct *arrayP = procArray;
|
|
int myoff;
|
|
int movecount;
|
|
|
|
#ifdef XIDCACHE_DEBUG
|
|
/* dump stats at backend shutdown, but not prepared-xact end */
|
|
if (proc->pid != 0)
|
|
DisplayXidCache();
|
|
#endif
|
|
|
|
/* See ProcGlobal comment explaining why both locks are held */
|
|
LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
|
|
LWLockAcquire(XidGenLock, LW_EXCLUSIVE);
|
|
|
|
myoff = proc->pgxactoff;
|
|
|
|
Assert(myoff >= 0 && myoff < arrayP->numProcs);
|
|
Assert(ProcGlobal->allProcs[arrayP->pgprocnos[myoff]].pgxactoff == myoff);
|
|
|
|
if (TransactionIdIsValid(latestXid))
|
|
{
|
|
Assert(TransactionIdIsValid(ProcGlobal->xids[myoff]));
|
|
|
|
/* Advance global latestCompletedXid while holding the lock */
|
|
MaintainLatestCompletedXid(latestXid);
|
|
|
|
/* Same with xactCompletionCount */
|
|
ShmemVariableCache->xactCompletionCount++;
|
|
|
|
ProcGlobal->xids[myoff] = InvalidTransactionId;
|
|
ProcGlobal->subxidStates[myoff].overflowed = false;
|
|
ProcGlobal->subxidStates[myoff].count = 0;
|
|
}
|
|
else
|
|
{
|
|
/* Shouldn't be trying to remove a live transaction here */
|
|
Assert(!TransactionIdIsValid(ProcGlobal->xids[myoff]));
|
|
}
|
|
|
|
Assert(!TransactionIdIsValid(ProcGlobal->xids[myoff]));
|
|
Assert(ProcGlobal->subxidStates[myoff].count == 0);
|
|
Assert(ProcGlobal->subxidStates[myoff].overflowed == false);
|
|
|
|
ProcGlobal->statusFlags[myoff] = 0;
|
|
|
|
/* Keep the PGPROC array sorted. See notes above */
|
|
movecount = arrayP->numProcs - myoff - 1;
|
|
memmove(&arrayP->pgprocnos[myoff],
|
|
&arrayP->pgprocnos[myoff + 1],
|
|
movecount * sizeof(*arrayP->pgprocnos));
|
|
memmove(&ProcGlobal->xids[myoff],
|
|
&ProcGlobal->xids[myoff + 1],
|
|
movecount * sizeof(*ProcGlobal->xids));
|
|
memmove(&ProcGlobal->subxidStates[myoff],
|
|
&ProcGlobal->subxidStates[myoff + 1],
|
|
movecount * sizeof(*ProcGlobal->subxidStates));
|
|
memmove(&ProcGlobal->statusFlags[myoff],
|
|
&ProcGlobal->statusFlags[myoff + 1],
|
|
movecount * sizeof(*ProcGlobal->statusFlags));
|
|
|
|
arrayP->pgprocnos[arrayP->numProcs - 1] = -1; /* for debugging */
|
|
arrayP->numProcs--;
|
|
|
|
/*
|
|
* Adjust pgxactoff of following procs for removed PGPROC (note that
|
|
* numProcs already has been decremented).
|
|
*/
|
|
for (int index = myoff; index < arrayP->numProcs; index++)
|
|
{
|
|
int procno = arrayP->pgprocnos[index];
|
|
|
|
Assert(procno >= 0 && procno < (arrayP->maxProcs + NUM_AUXILIARY_PROCS));
|
|
Assert(allProcs[procno].pgxactoff - 1 == index);
|
|
|
|
allProcs[procno].pgxactoff = index;
|
|
}
|
|
|
|
/*
|
|
* Release in reversed acquisition order, to reduce frequency of having to
|
|
* wait for XidGenLock while holding ProcArrayLock.
|
|
*/
|
|
LWLockRelease(XidGenLock);
|
|
LWLockRelease(ProcArrayLock);
|
|
}
|
|
|
|
|
|
/*
|
|
* ProcArrayEndTransaction -- mark a transaction as no longer running
|
|
*
|
|
* This is used interchangeably for commit and abort cases. The transaction
|
|
* commit/abort must already be reported to WAL and pg_xact.
|
|
*
|
|
* proc is currently always MyProc, but we pass it explicitly for flexibility.
|
|
* latestXid is the latest Xid among the transaction's main XID and
|
|
* subtransactions, or InvalidTransactionId if it has no XID. (We must ask
|
|
* the caller to pass latestXid, instead of computing it from the PGPROC's
|
|
* contents, because the subxid information in the PGPROC might be
|
|
* incomplete.)
|
|
*/
|
|
void
|
|
ProcArrayEndTransaction(PGPROC *proc, TransactionId latestXid)
|
|
{
|
|
if (TransactionIdIsValid(latestXid))
|
|
{
|
|
/*
|
|
* We must lock ProcArrayLock while clearing our advertised XID, so
|
|
* that we do not exit the set of "running" transactions while someone
|
|
* else is taking a snapshot. See discussion in
|
|
* src/backend/access/transam/README.
|
|
*/
|
|
Assert(TransactionIdIsValid(proc->xid));
|
|
|
|
/*
|
|
* If we can immediately acquire ProcArrayLock, we clear our own XID
|
|
* and release the lock. If not, use group XID clearing to improve
|
|
* efficiency.
|
|
*/
|
|
if (LWLockConditionalAcquire(ProcArrayLock, LW_EXCLUSIVE))
|
|
{
|
|
ProcArrayEndTransactionInternal(proc, latestXid);
|
|
LWLockRelease(ProcArrayLock);
|
|
}
|
|
else
|
|
ProcArrayGroupClearXid(proc, latestXid);
|
|
}
|
|
else
|
|
{
|
|
/*
|
|
* If we have no XID, we don't need to lock, since we won't affect
|
|
* anyone else's calculation of a snapshot. We might change their
|
|
* estimate of global xmin, but that's OK.
|
|
*/
|
|
Assert(!TransactionIdIsValid(proc->xid));
|
|
Assert(proc->subxidStatus.count == 0);
|
|
Assert(!proc->subxidStatus.overflowed);
|
|
|
|
proc->lxid = InvalidLocalTransactionId;
|
|
proc->xmin = InvalidTransactionId;
|
|
|
|
/* be sure this is cleared in abort */
|
|
proc->delayChkptFlags = 0;
|
|
|
|
proc->recoveryConflictPending = false;
|
|
|
|
/* must be cleared with xid/xmin: */
|
|
/* avoid unnecessarily dirtying shared cachelines */
|
|
if (proc->statusFlags & PROC_VACUUM_STATE_MASK)
|
|
{
|
|
Assert(!LWLockHeldByMe(ProcArrayLock));
|
|
LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
|
|
Assert(proc->statusFlags == ProcGlobal->statusFlags[proc->pgxactoff]);
|
|
proc->statusFlags &= ~PROC_VACUUM_STATE_MASK;
|
|
ProcGlobal->statusFlags[proc->pgxactoff] = proc->statusFlags;
|
|
LWLockRelease(ProcArrayLock);
|
|
}
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Mark a write transaction as no longer running.
|
|
*
|
|
* We don't do any locking here; caller must handle that.
|
|
*/
|
|
static inline void
|
|
ProcArrayEndTransactionInternal(PGPROC *proc, TransactionId latestXid)
|
|
{
|
|
int pgxactoff = proc->pgxactoff;
|
|
|
|
/*
|
|
* Note: we need exclusive lock here because we're going to change other
|
|
* processes' PGPROC entries.
|
|
*/
|
|
Assert(LWLockHeldByMeInMode(ProcArrayLock, LW_EXCLUSIVE));
|
|
Assert(TransactionIdIsValid(ProcGlobal->xids[pgxactoff]));
|
|
Assert(ProcGlobal->xids[pgxactoff] == proc->xid);
|
|
|
|
ProcGlobal->xids[pgxactoff] = InvalidTransactionId;
|
|
proc->xid = InvalidTransactionId;
|
|
proc->lxid = InvalidLocalTransactionId;
|
|
proc->xmin = InvalidTransactionId;
|
|
|
|
/* be sure this is cleared in abort */
|
|
proc->delayChkptFlags = 0;
|
|
|
|
proc->recoveryConflictPending = false;
|
|
|
|
/* must be cleared with xid/xmin: */
|
|
/* avoid unnecessarily dirtying shared cachelines */
|
|
if (proc->statusFlags & PROC_VACUUM_STATE_MASK)
|
|
{
|
|
proc->statusFlags &= ~PROC_VACUUM_STATE_MASK;
|
|
ProcGlobal->statusFlags[proc->pgxactoff] = proc->statusFlags;
|
|
}
|
|
|
|
/* Clear the subtransaction-XID cache too while holding the lock */
|
|
Assert(ProcGlobal->subxidStates[pgxactoff].count == proc->subxidStatus.count &&
|
|
ProcGlobal->subxidStates[pgxactoff].overflowed == proc->subxidStatus.overflowed);
|
|
if (proc->subxidStatus.count > 0 || proc->subxidStatus.overflowed)
|
|
{
|
|
ProcGlobal->subxidStates[pgxactoff].count = 0;
|
|
ProcGlobal->subxidStates[pgxactoff].overflowed = false;
|
|
proc->subxidStatus.count = 0;
|
|
proc->subxidStatus.overflowed = false;
|
|
}
|
|
|
|
/* Also advance global latestCompletedXid while holding the lock */
|
|
MaintainLatestCompletedXid(latestXid);
|
|
|
|
/* Same with xactCompletionCount */
|
|
ShmemVariableCache->xactCompletionCount++;
|
|
}
|
|
|
|
/*
|
|
* ProcArrayGroupClearXid -- group XID clearing
|
|
*
|
|
* When we cannot immediately acquire ProcArrayLock in exclusive mode at
|
|
* commit time, add ourselves to a list of processes that need their XIDs
|
|
* cleared. The first process to add itself to the list will acquire
|
|
* ProcArrayLock in exclusive mode and perform ProcArrayEndTransactionInternal
|
|
* on behalf of all group members. This avoids a great deal of contention
|
|
* around ProcArrayLock when many processes are trying to commit at once,
|
|
* since the lock need not be repeatedly handed off from one committing
|
|
* process to the next.
|
|
*/
|
|
static void
|
|
ProcArrayGroupClearXid(PGPROC *proc, TransactionId latestXid)
|
|
{
|
|
PROC_HDR *procglobal = ProcGlobal;
|
|
uint32 nextidx;
|
|
uint32 wakeidx;
|
|
|
|
/* We should definitely have an XID to clear. */
|
|
Assert(TransactionIdIsValid(proc->xid));
|
|
|
|
/* Add ourselves to the list of processes needing a group XID clear. */
|
|
proc->procArrayGroupMember = true;
|
|
proc->procArrayGroupMemberXid = latestXid;
|
|
nextidx = pg_atomic_read_u32(&procglobal->procArrayGroupFirst);
|
|
while (true)
|
|
{
|
|
pg_atomic_write_u32(&proc->procArrayGroupNext, nextidx);
|
|
|
|
if (pg_atomic_compare_exchange_u32(&procglobal->procArrayGroupFirst,
|
|
&nextidx,
|
|
(uint32) proc->pgprocno))
|
|
break;
|
|
}
|
|
|
|
/*
|
|
* If the list was not empty, the leader will clear our XID. It is
|
|
* impossible to have followers without a leader because the first process
|
|
* that has added itself to the list will always have nextidx as
|
|
* INVALID_PGPROCNO.
|
|
*/
|
|
if (nextidx != INVALID_PGPROCNO)
|
|
{
|
|
int extraWaits = 0;
|
|
|
|
/* Sleep until the leader clears our XID. */
|
|
pgstat_report_wait_start(WAIT_EVENT_PROCARRAY_GROUP_UPDATE);
|
|
for (;;)
|
|
{
|
|
/* acts as a read barrier */
|
|
PGSemaphoreLock(proc->sem);
|
|
if (!proc->procArrayGroupMember)
|
|
break;
|
|
extraWaits++;
|
|
}
|
|
pgstat_report_wait_end();
|
|
|
|
Assert(pg_atomic_read_u32(&proc->procArrayGroupNext) == INVALID_PGPROCNO);
|
|
|
|
/* Fix semaphore count for any absorbed wakeups */
|
|
while (extraWaits-- > 0)
|
|
PGSemaphoreUnlock(proc->sem);
|
|
return;
|
|
}
|
|
|
|
/* We are the leader. Acquire the lock on behalf of everyone. */
|
|
LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
|
|
|
|
/*
|
|
* Now that we've got the lock, clear the list of processes waiting for
|
|
* group XID clearing, saving a pointer to the head of the list. Trying
|
|
* to pop elements one at a time could lead to an ABA problem.
|
|
*/
|
|
nextidx = pg_atomic_exchange_u32(&procglobal->procArrayGroupFirst,
|
|
INVALID_PGPROCNO);
|
|
|
|
/* Remember head of list so we can perform wakeups after dropping lock. */
|
|
wakeidx = nextidx;
|
|
|
|
/* Walk the list and clear all XIDs. */
|
|
while (nextidx != INVALID_PGPROCNO)
|
|
{
|
|
PGPROC *nextproc = &allProcs[nextidx];
|
|
|
|
ProcArrayEndTransactionInternal(nextproc, nextproc->procArrayGroupMemberXid);
|
|
|
|
/* Move to next proc in list. */
|
|
nextidx = pg_atomic_read_u32(&nextproc->procArrayGroupNext);
|
|
}
|
|
|
|
/* We're done with the lock now. */
|
|
LWLockRelease(ProcArrayLock);
|
|
|
|
/*
|
|
* Now that we've released the lock, go back and wake everybody up. We
|
|
* don't do this under the lock so as to keep lock hold times to a
|
|
* minimum. The system calls we need to perform to wake other processes
|
|
* up are probably much slower than the simple memory writes we did while
|
|
* holding the lock.
|
|
*/
|
|
while (wakeidx != INVALID_PGPROCNO)
|
|
{
|
|
PGPROC *nextproc = &allProcs[wakeidx];
|
|
|
|
wakeidx = pg_atomic_read_u32(&nextproc->procArrayGroupNext);
|
|
pg_atomic_write_u32(&nextproc->procArrayGroupNext, INVALID_PGPROCNO);
|
|
|
|
/* ensure all previous writes are visible before follower continues. */
|
|
pg_write_barrier();
|
|
|
|
nextproc->procArrayGroupMember = false;
|
|
|
|
if (nextproc != MyProc)
|
|
PGSemaphoreUnlock(nextproc->sem);
|
|
}
|
|
}
|
|
|
|
/*
|
|
* ProcArrayClearTransaction -- clear the transaction fields
|
|
*
|
|
* This is used after successfully preparing a 2-phase transaction. We are
|
|
* not actually reporting the transaction's XID as no longer running --- it
|
|
* will still appear as running because the 2PC's gxact is in the ProcArray
|
|
* too. We just have to clear out our own PGPROC.
|
|
*/
|
|
void
|
|
ProcArrayClearTransaction(PGPROC *proc)
|
|
{
|
|
int pgxactoff;
|
|
|
|
/*
|
|
* Currently we need to lock ProcArrayLock exclusively here, as we
|
|
* increment xactCompletionCount below. We also need it at least in shared
|
|
* mode for pgproc->pgxactoff to stay the same below.
|
|
*
|
|
* We could however, as this action does not actually change anyone's view
|
|
* of the set of running XIDs (our entry is duplicate with the gxact that
|
|
* has already been inserted into the ProcArray), lower the lock level to
|
|
* shared if we were to make xactCompletionCount an atomic variable. But
|
|
* that doesn't seem worth it currently, as a 2PC commit is heavyweight
|
|
* enough for this not to be the bottleneck. If it ever becomes a
|
|
* bottleneck it may also be worth considering to combine this with the
|
|
* subsequent ProcArrayRemove()
|
|
*/
|
|
LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
|
|
|
|
pgxactoff = proc->pgxactoff;
|
|
|
|
ProcGlobal->xids[pgxactoff] = InvalidTransactionId;
|
|
proc->xid = InvalidTransactionId;
|
|
|
|
proc->lxid = InvalidLocalTransactionId;
|
|
proc->xmin = InvalidTransactionId;
|
|
proc->recoveryConflictPending = false;
|
|
|
|
Assert(!(proc->statusFlags & PROC_VACUUM_STATE_MASK));
|
|
Assert(!proc->delayChkptFlags);
|
|
|
|
/*
|
|
* Need to increment completion count even though transaction hasn't
|
|
* really committed yet. The reason for that is that GetSnapshotData()
|
|
* omits the xid of the current transaction, thus without the increment we
|
|
* otherwise could end up reusing the snapshot later. Which would be bad,
|
|
* because it might not count the prepared transaction as running.
|
|
*/
|
|
ShmemVariableCache->xactCompletionCount++;
|
|
|
|
/* Clear the subtransaction-XID cache too */
|
|
Assert(ProcGlobal->subxidStates[pgxactoff].count == proc->subxidStatus.count &&
|
|
ProcGlobal->subxidStates[pgxactoff].overflowed == proc->subxidStatus.overflowed);
|
|
if (proc->subxidStatus.count > 0 || proc->subxidStatus.overflowed)
|
|
{
|
|
ProcGlobal->subxidStates[pgxactoff].count = 0;
|
|
ProcGlobal->subxidStates[pgxactoff].overflowed = false;
|
|
proc->subxidStatus.count = 0;
|
|
proc->subxidStatus.overflowed = false;
|
|
}
|
|
|
|
LWLockRelease(ProcArrayLock);
|
|
}
|
|
|
|
/*
|
|
* Update ShmemVariableCache->latestCompletedXid to point to latestXid if
|
|
* currently older.
|
|
*/
|
|
static void
|
|
MaintainLatestCompletedXid(TransactionId latestXid)
|
|
{
|
|
FullTransactionId cur_latest = ShmemVariableCache->latestCompletedXid;
|
|
|
|
Assert(FullTransactionIdIsValid(cur_latest));
|
|
Assert(!RecoveryInProgress());
|
|
Assert(LWLockHeldByMe(ProcArrayLock));
|
|
|
|
if (TransactionIdPrecedes(XidFromFullTransactionId(cur_latest), latestXid))
|
|
{
|
|
ShmemVariableCache->latestCompletedXid =
|
|
FullXidRelativeTo(cur_latest, latestXid);
|
|
}
|
|
|
|
Assert(IsBootstrapProcessingMode() ||
|
|
FullTransactionIdIsNormal(ShmemVariableCache->latestCompletedXid));
|
|
}
|
|
|
|
/*
|
|
* Same as MaintainLatestCompletedXid, except for use during WAL replay.
|
|
*/
|
|
static void
|
|
MaintainLatestCompletedXidRecovery(TransactionId latestXid)
|
|
{
|
|
FullTransactionId cur_latest = ShmemVariableCache->latestCompletedXid;
|
|
FullTransactionId rel;
|
|
|
|
Assert(AmStartupProcess() || !IsUnderPostmaster);
|
|
Assert(LWLockHeldByMe(ProcArrayLock));
|
|
|
|
/*
|
|
* Need a FullTransactionId to compare latestXid with. Can't rely on
|
|
* latestCompletedXid to be initialized in recovery. But in recovery it's
|
|
* safe to access nextXid without a lock for the startup process.
|
|
*/
|
|
rel = ShmemVariableCache->nextXid;
|
|
Assert(FullTransactionIdIsValid(ShmemVariableCache->nextXid));
|
|
|
|
if (!FullTransactionIdIsValid(cur_latest) ||
|
|
TransactionIdPrecedes(XidFromFullTransactionId(cur_latest), latestXid))
|
|
{
|
|
ShmemVariableCache->latestCompletedXid =
|
|
FullXidRelativeTo(rel, latestXid);
|
|
}
|
|
|
|
Assert(FullTransactionIdIsNormal(ShmemVariableCache->latestCompletedXid));
|
|
}
|
|
|
|
/*
|
|
* ProcArrayInitRecovery -- initialize recovery xid mgmt environment
|
|
*
|
|
* Remember up to where the startup process initialized the CLOG and subtrans
|
|
* so we can ensure it's initialized gaplessly up to the point where necessary
|
|
* while in recovery.
|
|
*/
|
|
void
|
|
ProcArrayInitRecovery(TransactionId initializedUptoXID)
|
|
{
|
|
Assert(standbyState == STANDBY_INITIALIZED);
|
|
Assert(TransactionIdIsNormal(initializedUptoXID));
|
|
|
|
/*
|
|
* we set latestObservedXid to the xid SUBTRANS has been initialized up
|
|
* to, so we can extend it from that point onwards in
|
|
* RecordKnownAssignedTransactionIds, and when we get consistent in
|
|
* ProcArrayApplyRecoveryInfo().
|
|
*/
|
|
latestObservedXid = initializedUptoXID;
|
|
TransactionIdRetreat(latestObservedXid);
|
|
}
|
|
|
|
/*
|
|
* ProcArrayApplyRecoveryInfo -- apply recovery info about xids
|
|
*
|
|
* Takes us through 3 states: Initialized, Pending and Ready.
|
|
* Normal case is to go all the way to Ready straight away, though there
|
|
* are atypical cases where we need to take it in steps.
|
|
*
|
|
* Use the data about running transactions on the primary to create the initial
|
|
* state of KnownAssignedXids. We also use these records to regularly prune
|
|
* KnownAssignedXids because we know it is possible that some transactions
|
|
* with FATAL errors fail to write abort records, which could cause eventual
|
|
* overflow.
|
|
*
|
|
* See comments for LogStandbySnapshot().
|
|
*/
|
|
void
|
|
ProcArrayApplyRecoveryInfo(RunningTransactions running)
|
|
{
|
|
TransactionId *xids;
|
|
int nxids;
|
|
int i;
|
|
|
|
Assert(standbyState >= STANDBY_INITIALIZED);
|
|
Assert(TransactionIdIsValid(running->nextXid));
|
|
Assert(TransactionIdIsValid(running->oldestRunningXid));
|
|
Assert(TransactionIdIsNormal(running->latestCompletedXid));
|
|
|
|
/*
|
|
* Remove stale transactions, if any.
|
|
*/
|
|
ExpireOldKnownAssignedTransactionIds(running->oldestRunningXid);
|
|
|
|
/*
|
|
* Remove stale locks, if any.
|
|
*/
|
|
StandbyReleaseOldLocks(running->oldestRunningXid);
|
|
|
|
/*
|
|
* If our snapshot is already valid, nothing else to do...
|
|
*/
|
|
if (standbyState == STANDBY_SNAPSHOT_READY)
|
|
return;
|
|
|
|
/*
|
|
* If our initial RunningTransactionsData had an overflowed snapshot then
|
|
* we knew we were missing some subxids from our snapshot. If we continue
|
|
* to see overflowed snapshots then we might never be able to start up, so
|
|
* we make another test to see if our snapshot is now valid. We know that
|
|
* the missing subxids are equal to or earlier than nextXid. After we
|
|
* initialise we continue to apply changes during recovery, so once the
|
|
* oldestRunningXid is later than the nextXid from the initial snapshot we
|
|
* know that we no longer have missing information and can mark the
|
|
* snapshot as valid.
|
|
*/
|
|
if (standbyState == STANDBY_SNAPSHOT_PENDING)
|
|
{
|
|
/*
|
|
* If the snapshot isn't overflowed or if its empty we can reset our
|
|
* pending state and use this snapshot instead.
|
|
*/
|
|
if (!running->subxid_overflow || running->xcnt == 0)
|
|
{
|
|
/*
|
|
* If we have already collected known assigned xids, we need to
|
|
* throw them away before we apply the recovery snapshot.
|
|
*/
|
|
KnownAssignedXidsReset();
|
|
standbyState = STANDBY_INITIALIZED;
|
|
}
|
|
else
|
|
{
|
|
if (TransactionIdPrecedes(standbySnapshotPendingXmin,
|
|
running->oldestRunningXid))
|
|
{
|
|
standbyState = STANDBY_SNAPSHOT_READY;
|
|
elog(trace_recovery(DEBUG1),
|
|
"recovery snapshots are now enabled");
|
|
}
|
|
else
|
|
elog(trace_recovery(DEBUG1),
|
|
"recovery snapshot waiting for non-overflowed snapshot or "
|
|
"until oldest active xid on standby is at least %u (now %u)",
|
|
standbySnapshotPendingXmin,
|
|
running->oldestRunningXid);
|
|
return;
|
|
}
|
|
}
|
|
|
|
Assert(standbyState == STANDBY_INITIALIZED);
|
|
|
|
/*
|
|
* NB: this can be reached at least twice, so make sure new code can deal
|
|
* with that.
|
|
*/
|
|
|
|
/*
|
|
* Nobody else is running yet, but take locks anyhow
|
|
*/
|
|
LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
|
|
|
|
/*
|
|
* KnownAssignedXids is sorted so we cannot just add the xids, we have to
|
|
* sort them first.
|
|
*
|
|
* Some of the new xids are top-level xids and some are subtransactions.
|
|
* We don't call SubTransSetParent because it doesn't matter yet. If we
|
|
* aren't overflowed then all xids will fit in snapshot and so we don't
|
|
* need subtrans. If we later overflow, an xid assignment record will add
|
|
* xids to subtrans. If RunningTransactionsData is overflowed then we
|
|
* don't have enough information to correctly update subtrans anyway.
|
|
*/
|
|
|
|
/*
|
|
* Allocate a temporary array to avoid modifying the array passed as
|
|
* argument.
|
|
*/
|
|
xids = palloc(sizeof(TransactionId) * (running->xcnt + running->subxcnt));
|
|
|
|
/*
|
|
* Add to the temp array any xids which have not already completed.
|
|
*/
|
|
nxids = 0;
|
|
for (i = 0; i < running->xcnt + running->subxcnt; i++)
|
|
{
|
|
TransactionId xid = running->xids[i];
|
|
|
|
/*
|
|
* The running-xacts snapshot can contain xids that were still visible
|
|
* in the procarray when the snapshot was taken, but were already
|
|
* WAL-logged as completed. They're not running anymore, so ignore
|
|
* them.
|
|
*/
|
|
if (TransactionIdDidCommit(xid) || TransactionIdDidAbort(xid))
|
|
continue;
|
|
|
|
xids[nxids++] = xid;
|
|
}
|
|
|
|
if (nxids > 0)
|
|
{
|
|
if (procArray->numKnownAssignedXids != 0)
|
|
{
|
|
LWLockRelease(ProcArrayLock);
|
|
elog(ERROR, "KnownAssignedXids is not empty");
|
|
}
|
|
|
|
/*
|
|
* Sort the array so that we can add them safely into
|
|
* KnownAssignedXids.
|
|
*
|
|
* We have to sort them logically, because in KnownAssignedXidsAdd we
|
|
* call TransactionIdFollowsOrEquals and so on. But we know these XIDs
|
|
* come from RUNNING_XACTS, which means there are only normal XIDs
|
|
* from the same epoch, so this is safe.
|
|
*/
|
|
qsort(xids, nxids, sizeof(TransactionId), xidLogicalComparator);
|
|
|
|
/*
|
|
* Add the sorted snapshot into KnownAssignedXids. The running-xacts
|
|
* snapshot may include duplicated xids because of prepared
|
|
* transactions, so ignore them.
|
|
*/
|
|
for (i = 0; i < nxids; i++)
|
|
{
|
|
if (i > 0 && TransactionIdEquals(xids[i - 1], xids[i]))
|
|
{
|
|
elog(DEBUG1,
|
|
"found duplicated transaction %u for KnownAssignedXids insertion",
|
|
xids[i]);
|
|
continue;
|
|
}
|
|
KnownAssignedXidsAdd(xids[i], xids[i], true);
|
|
}
|
|
|
|
KnownAssignedXidsDisplay(trace_recovery(DEBUG3));
|
|
}
|
|
|
|
pfree(xids);
|
|
|
|
/*
|
|
* latestObservedXid is at least set to the point where SUBTRANS was
|
|
* started up to (cf. ProcArrayInitRecovery()) or to the biggest xid
|
|
* RecordKnownAssignedTransactionIds() was called for. Initialize
|
|
* subtrans from thereon, up to nextXid - 1.
|
|
*
|
|
* We need to duplicate parts of RecordKnownAssignedTransactionId() here,
|
|
* because we've just added xids to the known assigned xids machinery that
|
|
* haven't gone through RecordKnownAssignedTransactionId().
|
|
*/
|
|
Assert(TransactionIdIsNormal(latestObservedXid));
|
|
TransactionIdAdvance(latestObservedXid);
|
|
while (TransactionIdPrecedes(latestObservedXid, running->nextXid))
|
|
{
|
|
ExtendSUBTRANS(latestObservedXid);
|
|
TransactionIdAdvance(latestObservedXid);
|
|
}
|
|
TransactionIdRetreat(latestObservedXid); /* = running->nextXid - 1 */
|
|
|
|
/* ----------
|
|
* Now we've got the running xids we need to set the global values that
|
|
* are used to track snapshots as they evolve further.
|
|
*
|
|
* - latestCompletedXid which will be the xmax for snapshots
|
|
* - lastOverflowedXid which shows whether snapshots overflow
|
|
* - nextXid
|
|
*
|
|
* If the snapshot overflowed, then we still initialise with what we know,
|
|
* but the recovery snapshot isn't fully valid yet because we know there
|
|
* are some subxids missing. We don't know the specific subxids that are
|
|
* missing, so conservatively assume the last one is latestObservedXid.
|
|
* ----------
|
|
*/
|
|
if (running->subxid_overflow)
|
|
{
|
|
standbyState = STANDBY_SNAPSHOT_PENDING;
|
|
|
|
standbySnapshotPendingXmin = latestObservedXid;
|
|
procArray->lastOverflowedXid = latestObservedXid;
|
|
}
|
|
else
|
|
{
|
|
standbyState = STANDBY_SNAPSHOT_READY;
|
|
|
|
standbySnapshotPendingXmin = InvalidTransactionId;
|
|
}
|
|
|
|
/*
|
|
* If a transaction wrote a commit record in the gap between taking and
|
|
* logging the snapshot then latestCompletedXid may already be higher than
|
|
* the value from the snapshot, so check before we use the incoming value.
|
|
* It also might not yet be set at all.
|
|
*/
|
|
MaintainLatestCompletedXidRecovery(running->latestCompletedXid);
|
|
|
|
/*
|
|
* NB: No need to increment ShmemVariableCache->xactCompletionCount here,
|
|
* nobody can see it yet.
|
|
*/
|
|
|
|
LWLockRelease(ProcArrayLock);
|
|
|
|
/* ShmemVariableCache->nextXid must be beyond any observed xid. */
|
|
AdvanceNextFullTransactionIdPastXid(latestObservedXid);
|
|
|
|
Assert(FullTransactionIdIsValid(ShmemVariableCache->nextXid));
|
|
|
|
KnownAssignedXidsDisplay(trace_recovery(DEBUG3));
|
|
if (standbyState == STANDBY_SNAPSHOT_READY)
|
|
elog(trace_recovery(DEBUG1), "recovery snapshots are now enabled");
|
|
else
|
|
elog(trace_recovery(DEBUG1),
|
|
"recovery snapshot waiting for non-overflowed snapshot or "
|
|
"until oldest active xid on standby is at least %u (now %u)",
|
|
standbySnapshotPendingXmin,
|
|
running->oldestRunningXid);
|
|
}
|
|
|
|
/*
|
|
* ProcArrayApplyXidAssignment
|
|
* Process an XLOG_XACT_ASSIGNMENT WAL record
|
|
*/
|
|
void
|
|
ProcArrayApplyXidAssignment(TransactionId topxid,
|
|
int nsubxids, TransactionId *subxids)
|
|
{
|
|
TransactionId max_xid;
|
|
int i;
|
|
|
|
Assert(standbyState >= STANDBY_INITIALIZED);
|
|
|
|
max_xid = TransactionIdLatest(topxid, nsubxids, subxids);
|
|
|
|
/*
|
|
* Mark all the subtransactions as observed.
|
|
*
|
|
* NOTE: This will fail if the subxid contains too many previously
|
|
* unobserved xids to fit into known-assigned-xids. That shouldn't happen
|
|
* as the code stands, because xid-assignment records should never contain
|
|
* more than PGPROC_MAX_CACHED_SUBXIDS entries.
|
|
*/
|
|
RecordKnownAssignedTransactionIds(max_xid);
|
|
|
|
/*
|
|
* Notice that we update pg_subtrans with the top-level xid, rather than
|
|
* the parent xid. This is a difference between normal processing and
|
|
* recovery, yet is still correct in all cases. The reason is that
|
|
* subtransaction commit is not marked in clog until commit processing, so
|
|
* all aborted subtransactions have already been clearly marked in clog.
|
|
* As a result we are able to refer directly to the top-level
|
|
* transaction's state rather than skipping through all the intermediate
|
|
* states in the subtransaction tree. This should be the first time we
|
|
* have attempted to SubTransSetParent().
|
|
*/
|
|
for (i = 0; i < nsubxids; i++)
|
|
SubTransSetParent(subxids[i], topxid);
|
|
|
|
/* KnownAssignedXids isn't maintained yet, so we're done for now */
|
|
if (standbyState == STANDBY_INITIALIZED)
|
|
return;
|
|
|
|
/*
|
|
* Uses same locking as transaction commit
|
|
*/
|
|
LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
|
|
|
|
/*
|
|
* Remove subxids from known-assigned-xacts.
|
|
*/
|
|
KnownAssignedXidsRemoveTree(InvalidTransactionId, nsubxids, subxids);
|
|
|
|
/*
|
|
* Advance lastOverflowedXid to be at least the last of these subxids.
|
|
*/
|
|
if (TransactionIdPrecedes(procArray->lastOverflowedXid, max_xid))
|
|
procArray->lastOverflowedXid = max_xid;
|
|
|
|
LWLockRelease(ProcArrayLock);
|
|
}
|
|
|
|
/*
|
|
* TransactionIdIsInProgress -- is given transaction running in some backend
|
|
*
|
|
* Aside from some shortcuts such as checking RecentXmin and our own Xid,
|
|
* there are four possibilities for finding a running transaction:
|
|
*
|
|
* 1. The given Xid is a main transaction Id. We will find this out cheaply
|
|
* by looking at ProcGlobal->xids.
|
|
*
|
|
* 2. The given Xid is one of the cached subxact Xids in the PGPROC array.
|
|
* We can find this out cheaply too.
|
|
*
|
|
* 3. In Hot Standby mode, we must search the KnownAssignedXids list to see
|
|
* if the Xid is running on the primary.
|
|
*
|
|
* 4. Search the SubTrans tree to find the Xid's topmost parent, and then see
|
|
* if that is running according to ProcGlobal->xids[] or KnownAssignedXids.
|
|
* This is the slowest way, but sadly it has to be done always if the others
|
|
* failed, unless we see that the cached subxact sets are complete (none have
|
|
* overflowed).
|
|
*
|
|
* ProcArrayLock has to be held while we do 1, 2, 3. If we save the top Xids
|
|
* while doing 1 and 3, we can release the ProcArrayLock while we do 4.
|
|
* This buys back some concurrency (and we can't retrieve the main Xids from
|
|
* ProcGlobal->xids[] again anyway; see GetNewTransactionId).
|
|
*/
|
|
bool
|
|
TransactionIdIsInProgress(TransactionId xid)
|
|
{
|
|
static TransactionId *xids = NULL;
|
|
static TransactionId *other_xids;
|
|
XidCacheStatus *other_subxidstates;
|
|
int nxids = 0;
|
|
ProcArrayStruct *arrayP = procArray;
|
|
TransactionId topxid;
|
|
TransactionId latestCompletedXid;
|
|
int mypgxactoff;
|
|
int numProcs;
|
|
int j;
|
|
|
|
/*
|
|
* Don't bother checking a transaction older than RecentXmin; it could not
|
|
* possibly still be running. (Note: in particular, this guarantees that
|
|
* we reject InvalidTransactionId, FrozenTransactionId, etc as not
|
|
* running.)
|
|
*/
|
|
if (TransactionIdPrecedes(xid, RecentXmin))
|
|
{
|
|
xc_by_recent_xmin_inc();
|
|
return false;
|
|
}
|
|
|
|
/*
|
|
* We may have just checked the status of this transaction, so if it is
|
|
* already known to be completed, we can fall out without any access to
|
|
* shared memory.
|
|
*/
|
|
if (TransactionIdEquals(cachedXidIsNotInProgress, xid))
|
|
{
|
|
xc_by_known_xact_inc();
|
|
return false;
|
|
}
|
|
|
|
/*
|
|
* Also, we can handle our own transaction (and subtransactions) without
|
|
* any access to shared memory.
|
|
*/
|
|
if (TransactionIdIsCurrentTransactionId(xid))
|
|
{
|
|
xc_by_my_xact_inc();
|
|
return true;
|
|
}
|
|
|
|
/*
|
|
* If first time through, get workspace to remember main XIDs in. We
|
|
* malloc it permanently to avoid repeated palloc/pfree overhead.
|
|
*/
|
|
if (xids == NULL)
|
|
{
|
|
/*
|
|
* In hot standby mode, reserve enough space to hold all xids in the
|
|
* known-assigned list. If we later finish recovery, we no longer need
|
|
* the bigger array, but we don't bother to shrink it.
|
|
*/
|
|
int maxxids = RecoveryInProgress() ? TOTAL_MAX_CACHED_SUBXIDS : arrayP->maxProcs;
|
|
|
|
xids = (TransactionId *) malloc(maxxids * sizeof(TransactionId));
|
|
if (xids == NULL)
|
|
ereport(ERROR,
|
|
(errcode(ERRCODE_OUT_OF_MEMORY),
|
|
errmsg("out of memory")));
|
|
}
|
|
|
|
other_xids = ProcGlobal->xids;
|
|
other_subxidstates = ProcGlobal->subxidStates;
|
|
|
|
LWLockAcquire(ProcArrayLock, LW_SHARED);
|
|
|
|
/*
|
|
* Now that we have the lock, we can check latestCompletedXid; if the
|
|
* target Xid is after that, it's surely still running.
|
|
*/
|
|
latestCompletedXid =
|
|
XidFromFullTransactionId(ShmemVariableCache->latestCompletedXid);
|
|
if (TransactionIdPrecedes(latestCompletedXid, xid))
|
|
{
|
|
LWLockRelease(ProcArrayLock);
|
|
xc_by_latest_xid_inc();
|
|
return true;
|
|
}
|
|
|
|
/* No shortcuts, gotta grovel through the array */
|
|
mypgxactoff = MyProc->pgxactoff;
|
|
numProcs = arrayP->numProcs;
|
|
for (int pgxactoff = 0; pgxactoff < numProcs; pgxactoff++)
|
|
{
|
|
int pgprocno;
|
|
PGPROC *proc;
|
|
TransactionId pxid;
|
|
int pxids;
|
|
|
|
/* Ignore ourselves --- dealt with it above */
|
|
if (pgxactoff == mypgxactoff)
|
|
continue;
|
|
|
|
/* Fetch xid just once - see GetNewTransactionId */
|
|
pxid = UINT32_ACCESS_ONCE(other_xids[pgxactoff]);
|
|
|
|
if (!TransactionIdIsValid(pxid))
|
|
continue;
|
|
|
|
/*
|
|
* Step 1: check the main Xid
|
|
*/
|
|
if (TransactionIdEquals(pxid, xid))
|
|
{
|
|
LWLockRelease(ProcArrayLock);
|
|
xc_by_main_xid_inc();
|
|
return true;
|
|
}
|
|
|
|
/*
|
|
* We can ignore main Xids that are younger than the target Xid, since
|
|
* the target could not possibly be their child.
|
|
*/
|
|
if (TransactionIdPrecedes(xid, pxid))
|
|
continue;
|
|
|
|
/*
|
|
* Step 2: check the cached child-Xids arrays
|
|
*/
|
|
pxids = other_subxidstates[pgxactoff].count;
|
|
pg_read_barrier(); /* pairs with barrier in GetNewTransactionId() */
|
|
pgprocno = arrayP->pgprocnos[pgxactoff];
|
|
proc = &allProcs[pgprocno];
|
|
for (j = pxids - 1; j >= 0; j--)
|
|
{
|
|
/* Fetch xid just once - see GetNewTransactionId */
|
|
TransactionId cxid = UINT32_ACCESS_ONCE(proc->subxids.xids[j]);
|
|
|
|
if (TransactionIdEquals(cxid, xid))
|
|
{
|
|
LWLockRelease(ProcArrayLock);
|
|
xc_by_child_xid_inc();
|
|
return true;
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Save the main Xid for step 4. We only need to remember main Xids
|
|
* that have uncached children. (Note: there is no race condition
|
|
* here because the overflowed flag cannot be cleared, only set, while
|
|
* we hold ProcArrayLock. So we can't miss an Xid that we need to
|
|
* worry about.)
|
|
*/
|
|
if (other_subxidstates[pgxactoff].overflowed)
|
|
xids[nxids++] = pxid;
|
|
}
|
|
|
|
/*
|
|
* Step 3: in hot standby mode, check the known-assigned-xids list. XIDs
|
|
* in the list must be treated as running.
|
|
*/
|
|
if (RecoveryInProgress())
|
|
{
|
|
/* none of the PGPROC entries should have XIDs in hot standby mode */
|
|
Assert(nxids == 0);
|
|
|
|
if (KnownAssignedXidExists(xid))
|
|
{
|
|
LWLockRelease(ProcArrayLock);
|
|
xc_by_known_assigned_inc();
|
|
return true;
|
|
}
|
|
|
|
/*
|
|
* If the KnownAssignedXids overflowed, we have to check pg_subtrans
|
|
* too. Fetch all xids from KnownAssignedXids that are lower than
|
|
* xid, since if xid is a subtransaction its parent will always have a
|
|
* lower value. Note we will collect both main and subXIDs here, but
|
|
* there's no help for it.
|
|
*/
|
|
if (TransactionIdPrecedesOrEquals(xid, procArray->lastOverflowedXid))
|
|
nxids = KnownAssignedXidsGet(xids, xid);
|
|
}
|
|
|
|
LWLockRelease(ProcArrayLock);
|
|
|
|
/*
|
|
* If none of the relevant caches overflowed, we know the Xid is not
|
|
* running without even looking at pg_subtrans.
|
|
*/
|
|
if (nxids == 0)
|
|
{
|
|
xc_no_overflow_inc();
|
|
cachedXidIsNotInProgress = xid;
|
|
return false;
|
|
}
|
|
|
|
/*
|
|
* Step 4: have to check pg_subtrans.
|
|
*
|
|
* At this point, we know it's either a subtransaction of one of the Xids
|
|
* in xids[], or it's not running. If it's an already-failed
|
|
* subtransaction, we want to say "not running" even though its parent may
|
|
* still be running. So first, check pg_xact to see if it's been aborted.
|
|
*/
|
|
xc_slow_answer_inc();
|
|
|
|
if (TransactionIdDidAbort(xid))
|
|
{
|
|
cachedXidIsNotInProgress = xid;
|
|
return false;
|
|
}
|
|
|
|
/*
|
|
* It isn't aborted, so check whether the transaction tree it belongs to
|
|
* is still running (or, more precisely, whether it was running when we
|
|
* held ProcArrayLock).
|
|
*/
|
|
topxid = SubTransGetTopmostTransaction(xid);
|
|
Assert(TransactionIdIsValid(topxid));
|
|
if (!TransactionIdEquals(topxid, xid) &&
|
|
pg_lfind32(topxid, xids, nxids))
|
|
return true;
|
|
|
|
cachedXidIsNotInProgress = xid;
|
|
return false;
|
|
}
|
|
|
|
/*
|
|
* TransactionIdIsActive -- is xid the top-level XID of an active backend?
|
|
*
|
|
* This differs from TransactionIdIsInProgress in that it ignores prepared
|
|
* transactions, as well as transactions running on the primary if we're in
|
|
* hot standby. Also, we ignore subtransactions since that's not needed
|
|
* for current uses.
|
|
*/
|
|
bool
|
|
TransactionIdIsActive(TransactionId xid)
|
|
{
|
|
bool result = false;
|
|
ProcArrayStruct *arrayP = procArray;
|
|
TransactionId *other_xids = ProcGlobal->xids;
|
|
int i;
|
|
|
|
/*
|
|
* Don't bother checking a transaction older than RecentXmin; it could not
|
|
* possibly still be running.
|
|
*/
|
|
if (TransactionIdPrecedes(xid, RecentXmin))
|
|
return false;
|
|
|
|
LWLockAcquire(ProcArrayLock, LW_SHARED);
|
|
|
|
for (i = 0; i < arrayP->numProcs; i++)
|
|
{
|
|
int pgprocno = arrayP->pgprocnos[i];
|
|
PGPROC *proc = &allProcs[pgprocno];
|
|
TransactionId pxid;
|
|
|
|
/* Fetch xid just once - see GetNewTransactionId */
|
|
pxid = UINT32_ACCESS_ONCE(other_xids[i]);
|
|
|
|
if (!TransactionIdIsValid(pxid))
|
|
continue;
|
|
|
|
if (proc->pid == 0)
|
|
continue; /* ignore prepared transactions */
|
|
|
|
if (TransactionIdEquals(pxid, xid))
|
|
{
|
|
result = true;
|
|
break;
|
|
}
|
|
}
|
|
|
|
LWLockRelease(ProcArrayLock);
|
|
|
|
return result;
|
|
}
|
|
|
|
|
|
/*
|
|
* Determine XID horizons.
|
|
*
|
|
* This is used by wrapper functions like GetOldestNonRemovableTransactionId()
|
|
* (for VACUUM), GetReplicationHorizons() (for hot_standby_feedback), etc as
|
|
* well as "internally" by GlobalVisUpdate() (see comment above struct
|
|
* GlobalVisState).
|
|
*
|
|
* See the definition of ComputeXidHorizonsResult for the various computed
|
|
* horizons.
|
|
*
|
|
* For VACUUM separate horizons (used to decide which deleted tuples must
|
|
* be preserved), for shared and non-shared tables are computed. For shared
|
|
* relations backends in all databases must be considered, but for non-shared
|
|
* relations that's not required, since only backends in my own database could
|
|
* ever see the tuples in them. Also, we can ignore concurrently running lazy
|
|
* VACUUMs because (a) they must be working on other tables, and (b) they
|
|
* don't need to do snapshot-based lookups.
|
|
*
|
|
* This also computes a horizon used to truncate pg_subtrans. For that
|
|
* backends in all databases have to be considered, and concurrently running
|
|
* lazy VACUUMs cannot be ignored, as they still may perform pg_subtrans
|
|
* accesses.
|
|
*
|
|
* Note: we include all currently running xids in the set of considered xids.
|
|
* This ensures that if a just-started xact has not yet set its snapshot,
|
|
* when it does set the snapshot it cannot set xmin less than what we compute.
|
|
* See notes in src/backend/access/transam/README.
|
|
*
|
|
* Note: despite the above, it's possible for the calculated values to move
|
|
* backwards on repeated calls. The calculated values are conservative, so
|
|
* that anything older is definitely not considered as running by anyone
|
|
* anymore, but the exact values calculated depend on a number of things. For
|
|
* example, if there are no transactions running in the current database, the
|
|
* horizon for normal tables will be latestCompletedXid. If a transaction
|
|
* begins after that, its xmin will include in-progress transactions in other
|
|
* databases that started earlier, so another call will return a lower value.
|
|
* Nonetheless it is safe to vacuum a table in the current database with the
|
|
* first result. There are also replication-related effects: a walsender
|
|
* process can set its xmin based on transactions that are no longer running
|
|
* on the primary but are still being replayed on the standby, thus possibly
|
|
* making the values go backwards. In this case there is a possibility that
|
|
* we lose data that the standby would like to have, but unless the standby
|
|
* uses a replication slot to make its xmin persistent there is little we can
|
|
* do about that --- data is only protected if the walsender runs continuously
|
|
* while queries are executed on the standby. (The Hot Standby code deals
|
|
* with such cases by failing standby queries that needed to access
|
|
* already-removed data, so there's no integrity bug.)
|
|
*
|
|
* Note: the approximate horizons (see definition of GlobalVisState) are
|
|
* updated by the computations done here. That's currently required for
|
|
* correctness and a small optimization. Without doing so it's possible that
|
|
* heap vacuum's call to heap_page_prune() uses a more conservative horizon
|
|
* than later when deciding which tuples can be removed - which the code
|
|
* doesn't expect (breaking HOT).
|
|
*/
|
|
static void
|
|
ComputeXidHorizons(ComputeXidHorizonsResult *h)
|
|
{
|
|
ProcArrayStruct *arrayP = procArray;
|
|
TransactionId kaxmin;
|
|
bool in_recovery = RecoveryInProgress();
|
|
TransactionId *other_xids = ProcGlobal->xids;
|
|
|
|
/* inferred after ProcArrayLock is released */
|
|
h->catalog_oldest_nonremovable = InvalidTransactionId;
|
|
|
|
LWLockAcquire(ProcArrayLock, LW_SHARED);
|
|
|
|
h->latest_completed = ShmemVariableCache->latestCompletedXid;
|
|
|
|
/*
|
|
* We initialize the MIN() calculation with latestCompletedXid + 1. This
|
|
* is a lower bound for the XIDs that might appear in the ProcArray later,
|
|
* and so protects us against overestimating the result due to future
|
|
* additions.
|
|
*/
|
|
{
|
|
TransactionId initial;
|
|
|
|
initial = XidFromFullTransactionId(h->latest_completed);
|
|
Assert(TransactionIdIsValid(initial));
|
|
TransactionIdAdvance(initial);
|
|
|
|
h->oldest_considered_running = initial;
|
|
h->shared_oldest_nonremovable = initial;
|
|
h->data_oldest_nonremovable = initial;
|
|
|
|
/*
|
|
* Only modifications made by this backend affect the horizon for
|
|
* temporary relations. Instead of a check in each iteration of the
|
|
* loop over all PGPROCs it is cheaper to just initialize to the
|
|
* current top-level xid any.
|
|
*
|
|
* Without an assigned xid we could use a horizon as aggressive as
|
|
* GetNewTransactionId(), but we can get away with the much cheaper
|
|
* latestCompletedXid + 1: If this backend has no xid there, by
|
|
* definition, can't be any newer changes in the temp table than
|
|
* latestCompletedXid.
|
|
*/
|
|
if (TransactionIdIsValid(MyProc->xid))
|
|
h->temp_oldest_nonremovable = MyProc->xid;
|
|
else
|
|
h->temp_oldest_nonremovable = initial;
|
|
}
|
|
|
|
/*
|
|
* Fetch slot horizons while ProcArrayLock is held - the
|
|
* LWLockAcquire/LWLockRelease are a barrier, ensuring this happens inside
|
|
* the lock.
|
|
*/
|
|
h->slot_xmin = procArray->replication_slot_xmin;
|
|
h->slot_catalog_xmin = procArray->replication_slot_catalog_xmin;
|
|
|
|
for (int index = 0; index < arrayP->numProcs; index++)
|
|
{
|
|
int pgprocno = arrayP->pgprocnos[index];
|
|
PGPROC *proc = &allProcs[pgprocno];
|
|
int8 statusFlags = ProcGlobal->statusFlags[index];
|
|
TransactionId xid;
|
|
TransactionId xmin;
|
|
|
|
/* Fetch xid just once - see GetNewTransactionId */
|
|
xid = UINT32_ACCESS_ONCE(other_xids[index]);
|
|
xmin = UINT32_ACCESS_ONCE(proc->xmin);
|
|
|
|
/*
|
|
* Consider both the transaction's Xmin, and its Xid.
|
|
*
|
|
* We must check both because a transaction might have an Xmin but not
|
|
* (yet) an Xid; conversely, if it has an Xid, that could determine
|
|
* some not-yet-set Xmin.
|
|
*/
|
|
xmin = TransactionIdOlder(xmin, xid);
|
|
|
|
/* if neither is set, this proc doesn't influence the horizon */
|
|
if (!TransactionIdIsValid(xmin))
|
|
continue;
|
|
|
|
/*
|
|
* Don't ignore any procs when determining which transactions might be
|
|
* considered running. While slots should ensure logical decoding
|
|
* backends are protected even without this check, it can't hurt to
|
|
* include them here as well..
|
|
*/
|
|
h->oldest_considered_running =
|
|
TransactionIdOlder(h->oldest_considered_running, xmin);
|
|
|
|
/*
|
|
* Skip over backends either vacuuming (which is ok with rows being
|
|
* removed, as long as pg_subtrans is not truncated) or doing logical
|
|
* decoding (which manages xmin separately, check below).
|
|
*/
|
|
if (statusFlags & (PROC_IN_VACUUM | PROC_IN_LOGICAL_DECODING))
|
|
continue;
|
|
|
|
/* shared tables need to take backends in all databases into account */
|
|
h->shared_oldest_nonremovable =
|
|
TransactionIdOlder(h->shared_oldest_nonremovable, xmin);
|
|
|
|
/*
|
|
* Normally sessions in other databases are ignored for anything but
|
|
* the shared horizon.
|
|
*
|
|
* However, include them when MyDatabaseId is not (yet) set. A
|
|
* backend in the process of starting up must not compute a "too
|
|
* aggressive" horizon, otherwise we could end up using it to prune
|
|
* still-needed data away. If the current backend never connects to a
|
|
* database this is harmless, because data_oldest_nonremovable will
|
|
* never be utilized.
|
|
*
|
|
* Also, sessions marked with PROC_AFFECTS_ALL_HORIZONS should always
|
|
* be included. (This flag is used for hot standby feedback, which
|
|
* can't be tied to a specific database.)
|
|
*
|
|
* Also, while in recovery we cannot compute an accurate per-database
|
|
* horizon, as all xids are managed via the KnownAssignedXids
|
|
* machinery.
|
|
*/
|
|
if (proc->databaseId == MyDatabaseId ||
|
|
MyDatabaseId == InvalidOid ||
|
|
(statusFlags & PROC_AFFECTS_ALL_HORIZONS) ||
|
|
in_recovery)
|
|
{
|
|
h->data_oldest_nonremovable =
|
|
TransactionIdOlder(h->data_oldest_nonremovable, xmin);
|
|
}
|
|
}
|
|
|
|
/*
|
|
* If in recovery fetch oldest xid in KnownAssignedXids, will be applied
|
|
* after lock is released.
|
|
*/
|
|
if (in_recovery)
|
|
kaxmin = KnownAssignedXidsGetOldestXmin();
|
|
|
|
/*
|
|
* No other information from shared state is needed, release the lock
|
|
* immediately. The rest of the computations can be done without a lock.
|
|
*/
|
|
LWLockRelease(ProcArrayLock);
|
|
|
|
if (in_recovery)
|
|
{
|
|
h->oldest_considered_running =
|
|
TransactionIdOlder(h->oldest_considered_running, kaxmin);
|
|
h->shared_oldest_nonremovable =
|
|
TransactionIdOlder(h->shared_oldest_nonremovable, kaxmin);
|
|
h->data_oldest_nonremovable =
|
|
TransactionIdOlder(h->data_oldest_nonremovable, kaxmin);
|
|
/* temp relations cannot be accessed in recovery */
|
|
}
|
|
|
|
Assert(TransactionIdPrecedesOrEquals(h->oldest_considered_running,
|
|
h->shared_oldest_nonremovable));
|
|
Assert(TransactionIdPrecedesOrEquals(h->shared_oldest_nonremovable,
|
|
h->data_oldest_nonremovable));
|
|
|
|
/*
|
|
* Check whether there are replication slots requiring an older xmin.
|
|
*/
|
|
h->shared_oldest_nonremovable =
|
|
TransactionIdOlder(h->shared_oldest_nonremovable, h->slot_xmin);
|
|
h->data_oldest_nonremovable =
|
|
TransactionIdOlder(h->data_oldest_nonremovable, h->slot_xmin);
|
|
|
|
/*
|
|
* The only difference between catalog / data horizons is that the slot's
|
|
* catalog xmin is applied to the catalog one (so catalogs can be accessed
|
|
* for logical decoding). Initialize with data horizon, and then back up
|
|
* further if necessary. Have to back up the shared horizon as well, since
|
|
* that also can contain catalogs.
|
|
*/
|
|
h->shared_oldest_nonremovable_raw = h->shared_oldest_nonremovable;
|
|
h->shared_oldest_nonremovable =
|
|
TransactionIdOlder(h->shared_oldest_nonremovable,
|
|
h->slot_catalog_xmin);
|
|
h->catalog_oldest_nonremovable = h->data_oldest_nonremovable;
|
|
h->catalog_oldest_nonremovable =
|
|
TransactionIdOlder(h->catalog_oldest_nonremovable,
|
|
h->slot_catalog_xmin);
|
|
|
|
/*
|
|
* It's possible that slots backed up the horizons further than
|
|
* oldest_considered_running. Fix.
|
|
*/
|
|
h->oldest_considered_running =
|
|
TransactionIdOlder(h->oldest_considered_running,
|
|
h->shared_oldest_nonremovable);
|
|
h->oldest_considered_running =
|
|
TransactionIdOlder(h->oldest_considered_running,
|
|
h->catalog_oldest_nonremovable);
|
|
h->oldest_considered_running =
|
|
TransactionIdOlder(h->oldest_considered_running,
|
|
h->data_oldest_nonremovable);
|
|
|
|
/*
|
|
* shared horizons have to be at least as old as the oldest visible in
|
|
* current db
|
|
*/
|
|
Assert(TransactionIdPrecedesOrEquals(h->shared_oldest_nonremovable,
|
|
h->data_oldest_nonremovable));
|
|
Assert(TransactionIdPrecedesOrEquals(h->shared_oldest_nonremovable,
|
|
h->catalog_oldest_nonremovable));
|
|
|
|
/*
|
|
* Horizons need to ensure that pg_subtrans access is still possible for
|
|
* the relevant backends.
|
|
*/
|
|
Assert(TransactionIdPrecedesOrEquals(h->oldest_considered_running,
|
|
h->shared_oldest_nonremovable));
|
|
Assert(TransactionIdPrecedesOrEquals(h->oldest_considered_running,
|
|
h->catalog_oldest_nonremovable));
|
|
Assert(TransactionIdPrecedesOrEquals(h->oldest_considered_running,
|
|
h->data_oldest_nonremovable));
|
|
Assert(TransactionIdPrecedesOrEquals(h->oldest_considered_running,
|
|
h->temp_oldest_nonremovable));
|
|
Assert(!TransactionIdIsValid(h->slot_xmin) ||
|
|
TransactionIdPrecedesOrEquals(h->oldest_considered_running,
|
|
h->slot_xmin));
|
|
Assert(!TransactionIdIsValid(h->slot_catalog_xmin) ||
|
|
TransactionIdPrecedesOrEquals(h->oldest_considered_running,
|
|
h->slot_catalog_xmin));
|
|
|
|
/* update approximate horizons with the computed horizons */
|
|
GlobalVisUpdateApply(h);
|
|
}
|
|
|
|
/*
|
|
* Determine what kind of visibility horizon needs to be used for a
|
|
* relation. If rel is NULL, the most conservative horizon is used.
|
|
*/
|
|
static inline GlobalVisHorizonKind
|
|
GlobalVisHorizonKindForRel(Relation rel)
|
|
{
|
|
/*
|
|
* Other relkinds currently don't contain xids, nor always the necessary
|
|
* logical decoding markers.
|
|
*/
|
|
Assert(!rel ||
|
|
rel->rd_rel->relkind == RELKIND_RELATION ||
|
|
rel->rd_rel->relkind == RELKIND_MATVIEW ||
|
|
rel->rd_rel->relkind == RELKIND_TOASTVALUE);
|
|
|
|
if (rel == NULL || rel->rd_rel->relisshared || RecoveryInProgress())
|
|
return VISHORIZON_SHARED;
|
|
else if (IsCatalogRelation(rel) ||
|
|
RelationIsAccessibleInLogicalDecoding(rel))
|
|
return VISHORIZON_CATALOG;
|
|
else if (!RELATION_IS_LOCAL(rel))
|
|
return VISHORIZON_DATA;
|
|
else
|
|
return VISHORIZON_TEMP;
|
|
}
|
|
|
|
/*
|
|
* Return the oldest XID for which deleted tuples must be preserved in the
|
|
* passed table.
|
|
*
|
|
* If rel is not NULL the horizon may be considerably more recent than
|
|
* otherwise (i.e. fewer tuples will be removable). In the NULL case a horizon
|
|
* that is correct (but not optimal) for all relations will be returned.
|
|
*
|
|
* This is used by VACUUM to decide which deleted tuples must be preserved in
|
|
* the passed in table.
|
|
*/
|
|
TransactionId
|
|
GetOldestNonRemovableTransactionId(Relation rel)
|
|
{
|
|
ComputeXidHorizonsResult horizons;
|
|
|
|
ComputeXidHorizons(&horizons);
|
|
|
|
switch (GlobalVisHorizonKindForRel(rel))
|
|
{
|
|
case VISHORIZON_SHARED:
|
|
return horizons.shared_oldest_nonremovable;
|
|
case VISHORIZON_CATALOG:
|
|
return horizons.catalog_oldest_nonremovable;
|
|
case VISHORIZON_DATA:
|
|
return horizons.data_oldest_nonremovable;
|
|
case VISHORIZON_TEMP:
|
|
return horizons.temp_oldest_nonremovable;
|
|
}
|
|
|
|
/* just to prevent compiler warnings */
|
|
return InvalidTransactionId;
|
|
}
|
|
|
|
/*
|
|
* Return the oldest transaction id any currently running backend might still
|
|
* consider running. This should not be used for visibility / pruning
|
|
* determinations (see GetOldestNonRemovableTransactionId()), but for
|
|
* decisions like up to where pg_subtrans can be truncated.
|
|
*/
|
|
TransactionId
|
|
GetOldestTransactionIdConsideredRunning(void)
|
|
{
|
|
ComputeXidHorizonsResult horizons;
|
|
|
|
ComputeXidHorizons(&horizons);
|
|
|
|
return horizons.oldest_considered_running;
|
|
}
|
|
|
|
/*
|
|
* Return the visibility horizons for a hot standby feedback message.
|
|
*/
|
|
void
|
|
GetReplicationHorizons(TransactionId *xmin, TransactionId *catalog_xmin)
|
|
{
|
|
ComputeXidHorizonsResult horizons;
|
|
|
|
ComputeXidHorizons(&horizons);
|
|
|
|
/*
|
|
* Don't want to use shared_oldest_nonremovable here, as that contains the
|
|
* effect of replication slot's catalog_xmin. We want to send a separate
|
|
* feedback for the catalog horizon, so the primary can remove data table
|
|
* contents more aggressively.
|
|
*/
|
|
*xmin = horizons.shared_oldest_nonremovable_raw;
|
|
*catalog_xmin = horizons.slot_catalog_xmin;
|
|
}
|
|
|
|
/*
|
|
* GetMaxSnapshotXidCount -- get max size for snapshot XID array
|
|
*
|
|
* We have to export this for use by snapmgr.c.
|
|
*/
|
|
int
|
|
GetMaxSnapshotXidCount(void)
|
|
{
|
|
return procArray->maxProcs;
|
|
}
|
|
|
|
/*
|
|
* GetMaxSnapshotSubxidCount -- get max size for snapshot sub-XID array
|
|
*
|
|
* We have to export this for use by snapmgr.c.
|
|
*/
|
|
int
|
|
GetMaxSnapshotSubxidCount(void)
|
|
{
|
|
return TOTAL_MAX_CACHED_SUBXIDS;
|
|
}
|
|
|
|
/*
|
|
* Initialize old_snapshot_threshold specific parts of a newly build snapshot.
|
|
*/
|
|
static void
|
|
GetSnapshotDataInitOldSnapshot(Snapshot snapshot)
|
|
{
|
|
if (!OldSnapshotThresholdActive())
|
|
{
|
|
/*
|
|
* If not using "snapshot too old" feature, fill related fields with
|
|
* dummy values that don't require any locking.
|
|
*/
|
|
snapshot->lsn = InvalidXLogRecPtr;
|
|
snapshot->whenTaken = 0;
|
|
}
|
|
else
|
|
{
|
|
/*
|
|
* Capture the current time and WAL stream location in case this
|
|
* snapshot becomes old enough to need to fall back on the special
|
|
* "old snapshot" logic.
|
|
*/
|
|
snapshot->lsn = GetXLogInsertRecPtr();
|
|
snapshot->whenTaken = GetSnapshotCurrentTimestamp();
|
|
MaintainOldSnapshotTimeMapping(snapshot->whenTaken, snapshot->xmin);
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Helper function for GetSnapshotData() that checks if the bulk of the
|
|
* visibility information in the snapshot is still valid. If so, it updates
|
|
* the fields that need to change and returns true. Otherwise it returns
|
|
* false.
|
|
*
|
|
* This very likely can be evolved to not need ProcArrayLock held (at very
|
|
* least in the case we already hold a snapshot), but that's for another day.
|
|
*/
|
|
static bool
|
|
GetSnapshotDataReuse(Snapshot snapshot)
|
|
{
|
|
uint64 curXactCompletionCount;
|
|
|
|
Assert(LWLockHeldByMe(ProcArrayLock));
|
|
|
|
if (unlikely(snapshot->snapXactCompletionCount == 0))
|
|
return false;
|
|
|
|
curXactCompletionCount = ShmemVariableCache->xactCompletionCount;
|
|
if (curXactCompletionCount != snapshot->snapXactCompletionCount)
|
|
return false;
|
|
|
|
/*
|
|
* If the current xactCompletionCount is still the same as it was at the
|
|
* time the snapshot was built, we can be sure that rebuilding the
|
|
* contents of the snapshot the hard way would result in the same snapshot
|
|
* contents:
|
|
*
|
|
* As explained in transam/README, the set of xids considered running by
|
|
* GetSnapshotData() cannot change while ProcArrayLock is held. Snapshot
|
|
* contents only depend on transactions with xids and xactCompletionCount
|
|
* is incremented whenever a transaction with an xid finishes (while
|
|
* holding ProcArrayLock) exclusively). Thus the xactCompletionCount check
|
|
* ensures we would detect if the snapshot would have changed.
|
|
*
|
|
* As the snapshot contents are the same as it was before, it is safe to
|
|
* re-enter the snapshot's xmin into the PGPROC array. None of the rows
|
|
* visible under the snapshot could already have been removed (that'd
|
|
* require the set of running transactions to change) and it fulfills the
|
|
* requirement that concurrent GetSnapshotData() calls yield the same
|
|
* xmin.
|
|
*/
|
|
if (!TransactionIdIsValid(MyProc->xmin))
|
|
MyProc->xmin = TransactionXmin = snapshot->xmin;
|
|
|
|
RecentXmin = snapshot->xmin;
|
|
Assert(TransactionIdPrecedesOrEquals(TransactionXmin, RecentXmin));
|
|
|
|
snapshot->curcid = GetCurrentCommandId(false);
|
|
snapshot->active_count = 0;
|
|
snapshot->regd_count = 0;
|
|
snapshot->copied = false;
|
|
|
|
GetSnapshotDataInitOldSnapshot(snapshot);
|
|
|
|
return true;
|
|
}
|
|
|
|
/*
|
|
* GetSnapshotData -- returns information about running transactions.
|
|
*
|
|
* The returned snapshot includes xmin (lowest still-running xact ID),
|
|
* xmax (highest completed xact ID + 1), and a list of running xact IDs
|
|
* in the range xmin <= xid < xmax. It is used as follows:
|
|
* All xact IDs < xmin are considered finished.
|
|
* All xact IDs >= xmax are considered still running.
|
|
* For an xact ID xmin <= xid < xmax, consult list to see whether
|
|
* it is considered running or not.
|
|
* This ensures that the set of transactions seen as "running" by the
|
|
* current xact will not change after it takes the snapshot.
|
|
*
|
|
* All running top-level XIDs are included in the snapshot, except for lazy
|
|
* VACUUM processes. We also try to include running subtransaction XIDs,
|
|
* but since PGPROC has only a limited cache area for subxact XIDs, full
|
|
* information may not be available. If we find any overflowed subxid arrays,
|
|
* we have to mark the snapshot's subxid data as overflowed, and extra work
|
|
* *may* need to be done to determine what's running (see XidInMVCCSnapshot()
|
|
* in heapam_visibility.c).
|
|
*
|
|
* We also update the following backend-global variables:
|
|
* TransactionXmin: the oldest xmin of any snapshot in use in the
|
|
* current transaction (this is the same as MyProc->xmin).
|
|
* RecentXmin: the xmin computed for the most recent snapshot. XIDs
|
|
* older than this are known not running any more.
|
|
*
|
|
* And try to advance the bounds of GlobalVis{Shared,Catalog,Data,Temp}Rels
|
|
* for the benefit of the GlobalVisTest* family of functions.
|
|
*
|
|
* Note: this function should probably not be called with an argument that's
|
|
* not statically allocated (see xip allocation below).
|
|
*/
|
|
Snapshot
|
|
GetSnapshotData(Snapshot snapshot)
|
|
{
|
|
ProcArrayStruct *arrayP = procArray;
|
|
TransactionId *other_xids = ProcGlobal->xids;
|
|
TransactionId xmin;
|
|
TransactionId xmax;
|
|
int count = 0;
|
|
int subcount = 0;
|
|
bool suboverflowed = false;
|
|
FullTransactionId latest_completed;
|
|
TransactionId oldestxid;
|
|
int mypgxactoff;
|
|
TransactionId myxid;
|
|
uint64 curXactCompletionCount;
|
|
|
|
TransactionId replication_slot_xmin = InvalidTransactionId;
|
|
TransactionId replication_slot_catalog_xmin = InvalidTransactionId;
|
|
|
|
Assert(snapshot != NULL);
|
|
|
|
/*
|
|
* Allocating space for maxProcs xids is usually overkill; numProcs would
|
|
* be sufficient. But it seems better to do the malloc while not holding
|
|
* the lock, so we can't look at numProcs. Likewise, we allocate much
|
|
* more subxip storage than is probably needed.
|
|
*
|
|
* This does open a possibility for avoiding repeated malloc/free: since
|
|
* maxProcs does not change at runtime, we can simply reuse the previous
|
|
* xip arrays if any. (This relies on the fact that all callers pass
|
|
* static SnapshotData structs.)
|
|
*/
|
|
if (snapshot->xip == NULL)
|
|
{
|
|
/*
|
|
* First call for this snapshot. Snapshot is same size whether or not
|
|
* we are in recovery, see later comments.
|
|
*/
|
|
snapshot->xip = (TransactionId *)
|
|
malloc(GetMaxSnapshotXidCount() * sizeof(TransactionId));
|
|
if (snapshot->xip == NULL)
|
|
ereport(ERROR,
|
|
(errcode(ERRCODE_OUT_OF_MEMORY),
|
|
errmsg("out of memory")));
|
|
Assert(snapshot->subxip == NULL);
|
|
snapshot->subxip = (TransactionId *)
|
|
malloc(GetMaxSnapshotSubxidCount() * sizeof(TransactionId));
|
|
if (snapshot->subxip == NULL)
|
|
ereport(ERROR,
|
|
(errcode(ERRCODE_OUT_OF_MEMORY),
|
|
errmsg("out of memory")));
|
|
}
|
|
|
|
/*
|
|
* It is sufficient to get shared lock on ProcArrayLock, even if we are
|
|
* going to set MyProc->xmin.
|
|
*/
|
|
LWLockAcquire(ProcArrayLock, LW_SHARED);
|
|
|
|
if (GetSnapshotDataReuse(snapshot))
|
|
{
|
|
LWLockRelease(ProcArrayLock);
|
|
return snapshot;
|
|
}
|
|
|
|
latest_completed = ShmemVariableCache->latestCompletedXid;
|
|
mypgxactoff = MyProc->pgxactoff;
|
|
myxid = other_xids[mypgxactoff];
|
|
Assert(myxid == MyProc->xid);
|
|
|
|
oldestxid = ShmemVariableCache->oldestXid;
|
|
curXactCompletionCount = ShmemVariableCache->xactCompletionCount;
|
|
|
|
/* xmax is always latestCompletedXid + 1 */
|
|
xmax = XidFromFullTransactionId(latest_completed);
|
|
TransactionIdAdvance(xmax);
|
|
Assert(TransactionIdIsNormal(xmax));
|
|
|
|
/* initialize xmin calculation with xmax */
|
|
xmin = xmax;
|
|
|
|
/* take own xid into account, saves a check inside the loop */
|
|
if (TransactionIdIsNormal(myxid) && NormalTransactionIdPrecedes(myxid, xmin))
|
|
xmin = myxid;
|
|
|
|
snapshot->takenDuringRecovery = RecoveryInProgress();
|
|
|
|
if (!snapshot->takenDuringRecovery)
|
|
{
|
|
int numProcs = arrayP->numProcs;
|
|
TransactionId *xip = snapshot->xip;
|
|
int *pgprocnos = arrayP->pgprocnos;
|
|
XidCacheStatus *subxidStates = ProcGlobal->subxidStates;
|
|
uint8 *allStatusFlags = ProcGlobal->statusFlags;
|
|
|
|
/*
|
|
* First collect set of pgxactoff/xids that need to be included in the
|
|
* snapshot.
|
|
*/
|
|
for (int pgxactoff = 0; pgxactoff < numProcs; pgxactoff++)
|
|
{
|
|
/* Fetch xid just once - see GetNewTransactionId */
|
|
TransactionId xid = UINT32_ACCESS_ONCE(other_xids[pgxactoff]);
|
|
uint8 statusFlags;
|
|
|
|
Assert(allProcs[arrayP->pgprocnos[pgxactoff]].pgxactoff == pgxactoff);
|
|
|
|
/*
|
|
* If the transaction has no XID assigned, we can skip it; it
|
|
* won't have sub-XIDs either.
|
|
*/
|
|
if (likely(xid == InvalidTransactionId))
|
|
continue;
|
|
|
|
/*
|
|
* We don't include our own XIDs (if any) in the snapshot. It
|
|
* needs to be included in the xmin computation, but we did so
|
|
* outside the loop.
|
|
*/
|
|
if (pgxactoff == mypgxactoff)
|
|
continue;
|
|
|
|
/*
|
|
* The only way we are able to get here with a non-normal xid is
|
|
* during bootstrap - with this backend using
|
|
* BootstrapTransactionId. But the above test should filter that
|
|
* out.
|
|
*/
|
|
Assert(TransactionIdIsNormal(xid));
|
|
|
|
/*
|
|
* If the XID is >= xmax, we can skip it; such transactions will
|
|
* be treated as running anyway (and any sub-XIDs will also be >=
|
|
* xmax).
|
|
*/
|
|
if (!NormalTransactionIdPrecedes(xid, xmax))
|
|
continue;
|
|
|
|
/*
|
|
* Skip over backends doing logical decoding which manages xmin
|
|
* separately (check below) and ones running LAZY VACUUM.
|
|
*/
|
|
statusFlags = allStatusFlags[pgxactoff];
|
|
if (statusFlags & (PROC_IN_LOGICAL_DECODING | PROC_IN_VACUUM))
|
|
continue;
|
|
|
|
if (NormalTransactionIdPrecedes(xid, xmin))
|
|
xmin = xid;
|
|
|
|
/* Add XID to snapshot. */
|
|
xip[count++] = xid;
|
|
|
|
/*
|
|
* Save subtransaction XIDs if possible (if we've already
|
|
* overflowed, there's no point). Note that the subxact XIDs must
|
|
* be later than their parent, so no need to check them against
|
|
* xmin. We could filter against xmax, but it seems better not to
|
|
* do that much work while holding the ProcArrayLock.
|
|
*
|
|
* The other backend can add more subxids concurrently, but cannot
|
|
* remove any. Hence it's important to fetch nxids just once.
|
|
* Should be safe to use memcpy, though. (We needn't worry about
|
|
* missing any xids added concurrently, because they must postdate
|
|
* xmax.)
|
|
*
|
|
* Again, our own XIDs are not included in the snapshot.
|
|
*/
|
|
if (!suboverflowed)
|
|
{
|
|
|
|
if (subxidStates[pgxactoff].overflowed)
|
|
suboverflowed = true;
|
|
else
|
|
{
|
|
int nsubxids = subxidStates[pgxactoff].count;
|
|
|
|
if (nsubxids > 0)
|
|
{
|
|
int pgprocno = pgprocnos[pgxactoff];
|
|
PGPROC *proc = &allProcs[pgprocno];
|
|
|
|
pg_read_barrier(); /* pairs with GetNewTransactionId */
|
|
|
|
memcpy(snapshot->subxip + subcount,
|
|
proc->subxids.xids,
|
|
nsubxids * sizeof(TransactionId));
|
|
subcount += nsubxids;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|
|
else
|
|
{
|
|
/*
|
|
* We're in hot standby, so get XIDs from KnownAssignedXids.
|
|
*
|
|
* We store all xids directly into subxip[]. Here's why:
|
|
*
|
|
* In recovery we don't know which xids are top-level and which are
|
|
* subxacts, a design choice that greatly simplifies xid processing.
|
|
*
|
|
* It seems like we would want to try to put xids into xip[] only, but
|
|
* that is fairly small. We would either need to make that bigger or
|
|
* to increase the rate at which we WAL-log xid assignment; neither is
|
|
* an appealing choice.
|
|
*
|
|
* We could try to store xids into xip[] first and then into subxip[]
|
|
* if there are too many xids. That only works if the snapshot doesn't
|
|
* overflow because we do not search subxip[] in that case. A simpler
|
|
* way is to just store all xids in the subxip array because this is
|
|
* by far the bigger array. We just leave the xip array empty.
|
|
*
|
|
* Either way we need to change the way XidInMVCCSnapshot() works
|
|
* depending upon when the snapshot was taken, or change normal
|
|
* snapshot processing so it matches.
|
|
*
|
|
* Note: It is possible for recovery to end before we finish taking
|
|
* the snapshot, and for newly assigned transaction ids to be added to
|
|
* the ProcArray. xmax cannot change while we hold ProcArrayLock, so
|
|
* those newly added transaction ids would be filtered away, so we
|
|
* need not be concerned about them.
|
|
*/
|
|
subcount = KnownAssignedXidsGetAndSetXmin(snapshot->subxip, &xmin,
|
|
xmax);
|
|
|
|
if (TransactionIdPrecedesOrEquals(xmin, procArray->lastOverflowedXid))
|
|
suboverflowed = true;
|
|
}
|
|
|
|
|
|
/*
|
|
* Fetch into local variable while ProcArrayLock is held - the
|
|
* LWLockRelease below is a barrier, ensuring this happens inside the
|
|
* lock.
|
|
*/
|
|
replication_slot_xmin = procArray->replication_slot_xmin;
|
|
replication_slot_catalog_xmin = procArray->replication_slot_catalog_xmin;
|
|
|
|
if (!TransactionIdIsValid(MyProc->xmin))
|
|
MyProc->xmin = TransactionXmin = xmin;
|
|
|
|
LWLockRelease(ProcArrayLock);
|
|
|
|
/* maintain state for GlobalVis* */
|
|
{
|
|
TransactionId def_vis_xid;
|
|
TransactionId def_vis_xid_data;
|
|
FullTransactionId def_vis_fxid;
|
|
FullTransactionId def_vis_fxid_data;
|
|
FullTransactionId oldestfxid;
|
|
|
|
/*
|
|
* Converting oldestXid is only safe when xid horizon cannot advance,
|
|
* i.e. holding locks. While we don't hold the lock anymore, all the
|
|
* necessary data has been gathered with lock held.
|
|
*/
|
|
oldestfxid = FullXidRelativeTo(latest_completed, oldestxid);
|
|
|
|
/* Check whether there's a replication slot requiring an older xmin. */
|
|
def_vis_xid_data =
|
|
TransactionIdOlder(xmin, replication_slot_xmin);
|
|
|
|
/*
|
|
* Rows in non-shared, non-catalog tables possibly could be vacuumed
|
|
* if older than this xid.
|
|
*/
|
|
def_vis_xid = def_vis_xid_data;
|
|
|
|
/*
|
|
* Check whether there's a replication slot requiring an older catalog
|
|
* xmin.
|
|
*/
|
|
def_vis_xid =
|
|
TransactionIdOlder(replication_slot_catalog_xmin, def_vis_xid);
|
|
|
|
def_vis_fxid = FullXidRelativeTo(latest_completed, def_vis_xid);
|
|
def_vis_fxid_data = FullXidRelativeTo(latest_completed, def_vis_xid_data);
|
|
|
|
/*
|
|
* Check if we can increase upper bound. As a previous
|
|
* GlobalVisUpdate() might have computed more aggressive values, don't
|
|
* overwrite them if so.
|
|
*/
|
|
GlobalVisSharedRels.definitely_needed =
|
|
FullTransactionIdNewer(def_vis_fxid,
|
|
GlobalVisSharedRels.definitely_needed);
|
|
GlobalVisCatalogRels.definitely_needed =
|
|
FullTransactionIdNewer(def_vis_fxid,
|
|
GlobalVisCatalogRels.definitely_needed);
|
|
GlobalVisDataRels.definitely_needed =
|
|
FullTransactionIdNewer(def_vis_fxid_data,
|
|
GlobalVisDataRels.definitely_needed);
|
|
/* See temp_oldest_nonremovable computation in ComputeXidHorizons() */
|
|
if (TransactionIdIsNormal(myxid))
|
|
GlobalVisTempRels.definitely_needed =
|
|
FullXidRelativeTo(latest_completed, myxid);
|
|
else
|
|
{
|
|
GlobalVisTempRels.definitely_needed = latest_completed;
|
|
FullTransactionIdAdvance(&GlobalVisTempRels.definitely_needed);
|
|
}
|
|
|
|
/*
|
|
* Check if we know that we can initialize or increase the lower
|
|
* bound. Currently the only cheap way to do so is to use
|
|
* ShmemVariableCache->oldestXid as input.
|
|
*
|
|
* We should definitely be able to do better. We could e.g. put a
|
|
* global lower bound value into ShmemVariableCache.
|
|
*/
|
|
GlobalVisSharedRels.maybe_needed =
|
|
FullTransactionIdNewer(GlobalVisSharedRels.maybe_needed,
|
|
oldestfxid);
|
|
GlobalVisCatalogRels.maybe_needed =
|
|
FullTransactionIdNewer(GlobalVisCatalogRels.maybe_needed,
|
|
oldestfxid);
|
|
GlobalVisDataRels.maybe_needed =
|
|
FullTransactionIdNewer(GlobalVisDataRels.maybe_needed,
|
|
oldestfxid);
|
|
/* accurate value known */
|
|
GlobalVisTempRels.maybe_needed = GlobalVisTempRels.definitely_needed;
|
|
}
|
|
|
|
RecentXmin = xmin;
|
|
Assert(TransactionIdPrecedesOrEquals(TransactionXmin, RecentXmin));
|
|
|
|
snapshot->xmin = xmin;
|
|
snapshot->xmax = xmax;
|
|
snapshot->xcnt = count;
|
|
snapshot->subxcnt = subcount;
|
|
snapshot->suboverflowed = suboverflowed;
|
|
snapshot->snapXactCompletionCount = curXactCompletionCount;
|
|
|
|
snapshot->curcid = GetCurrentCommandId(false);
|
|
|
|
/*
|
|
* This is a new snapshot, so set both refcounts are zero, and mark it as
|
|
* not copied in persistent memory.
|
|
*/
|
|
snapshot->active_count = 0;
|
|
snapshot->regd_count = 0;
|
|
snapshot->copied = false;
|
|
|
|
GetSnapshotDataInitOldSnapshot(snapshot);
|
|
|
|
return snapshot;
|
|
}
|
|
|
|
/*
|
|
* ProcArrayInstallImportedXmin -- install imported xmin into MyProc->xmin
|
|
*
|
|
* This is called when installing a snapshot imported from another
|
|
* transaction. To ensure that OldestXmin doesn't go backwards, we must
|
|
* check that the source transaction is still running, and we'd better do
|
|
* that atomically with installing the new xmin.
|
|
*
|
|
* Returns true if successful, false if source xact is no longer running.
|
|
*/
|
|
bool
|
|
ProcArrayInstallImportedXmin(TransactionId xmin,
|
|
VirtualTransactionId *sourcevxid)
|
|
{
|
|
bool result = false;
|
|
ProcArrayStruct *arrayP = procArray;
|
|
int index;
|
|
|
|
Assert(TransactionIdIsNormal(xmin));
|
|
if (!sourcevxid)
|
|
return false;
|
|
|
|
/* Get lock so source xact can't end while we're doing this */
|
|
LWLockAcquire(ProcArrayLock, LW_SHARED);
|
|
|
|
for (index = 0; index < arrayP->numProcs; index++)
|
|
{
|
|
int pgprocno = arrayP->pgprocnos[index];
|
|
PGPROC *proc = &allProcs[pgprocno];
|
|
int statusFlags = ProcGlobal->statusFlags[index];
|
|
TransactionId xid;
|
|
|
|
/* Ignore procs running LAZY VACUUM */
|
|
if (statusFlags & PROC_IN_VACUUM)
|
|
continue;
|
|
|
|
/* We are only interested in the specific virtual transaction. */
|
|
if (proc->backendId != sourcevxid->backendId)
|
|
continue;
|
|
if (proc->lxid != sourcevxid->localTransactionId)
|
|
continue;
|
|
|
|
/*
|
|
* We check the transaction's database ID for paranoia's sake: if it's
|
|
* in another DB then its xmin does not cover us. Caller should have
|
|
* detected this already, so we just treat any funny cases as
|
|
* "transaction not found".
|
|
*/
|
|
if (proc->databaseId != MyDatabaseId)
|
|
continue;
|
|
|
|
/*
|
|
* Likewise, let's just make real sure its xmin does cover us.
|
|
*/
|
|
xid = UINT32_ACCESS_ONCE(proc->xmin);
|
|
if (!TransactionIdIsNormal(xid) ||
|
|
!TransactionIdPrecedesOrEquals(xid, xmin))
|
|
continue;
|
|
|
|
/*
|
|
* We're good. Install the new xmin. As in GetSnapshotData, set
|
|
* TransactionXmin too. (Note that because snapmgr.c called
|
|
* GetSnapshotData first, we'll be overwriting a valid xmin here, so
|
|
* we don't check that.)
|
|
*/
|
|
MyProc->xmin = TransactionXmin = xmin;
|
|
|
|
result = true;
|
|
break;
|
|
}
|
|
|
|
LWLockRelease(ProcArrayLock);
|
|
|
|
return result;
|
|
}
|
|
|
|
/*
|
|
* ProcArrayInstallRestoredXmin -- install restored xmin into MyProc->xmin
|
|
*
|
|
* This is like ProcArrayInstallImportedXmin, but we have a pointer to the
|
|
* PGPROC of the transaction from which we imported the snapshot, rather than
|
|
* an XID.
|
|
*
|
|
* Note that this function also copies statusFlags from the source `proc` in
|
|
* order to avoid the case where MyProc's xmin needs to be skipped for
|
|
* computing xid horizon.
|
|
*
|
|
* Returns true if successful, false if source xact is no longer running.
|
|
*/
|
|
bool
|
|
ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
|
|
{
|
|
bool result = false;
|
|
TransactionId xid;
|
|
|
|
Assert(TransactionIdIsNormal(xmin));
|
|
Assert(proc != NULL);
|
|
|
|
/*
|
|
* Get an exclusive lock so that we can copy statusFlags from source proc.
|
|
*/
|
|
LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
|
|
|
|
/*
|
|
* Be certain that the referenced PGPROC has an advertised xmin which is
|
|
* no later than the one we're installing, so that the system-wide xmin
|
|
* can't go backwards. Also, make sure it's running in the same database,
|
|
* so that the per-database xmin cannot go backwards.
|
|
*/
|
|
xid = UINT32_ACCESS_ONCE(proc->xmin);
|
|
if (proc->databaseId == MyDatabaseId &&
|
|
TransactionIdIsNormal(xid) &&
|
|
TransactionIdPrecedesOrEquals(xid, xmin))
|
|
{
|
|
/*
|
|
* Install xmin and propagate the statusFlags that affect how the
|
|
* value is interpreted by vacuum.
|
|
*/
|
|
MyProc->xmin = TransactionXmin = xmin;
|
|
MyProc->statusFlags = (MyProc->statusFlags & ~PROC_XMIN_FLAGS) |
|
|
(proc->statusFlags & PROC_XMIN_FLAGS);
|
|
ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags;
|
|
|
|
result = true;
|
|
}
|
|
|
|
LWLockRelease(ProcArrayLock);
|
|
|
|
return result;
|
|
}
|
|
|
|
/*
|
|
* GetRunningTransactionData -- returns information about running transactions.
|
|
*
|
|
* Similar to GetSnapshotData but returns more information. We include
|
|
* all PGPROCs with an assigned TransactionId, even VACUUM processes and
|
|
* prepared transactions.
|
|
*
|
|
* We acquire XidGenLock and ProcArrayLock, but the caller is responsible for
|
|
* releasing them. Acquiring XidGenLock ensures that no new XIDs enter the proc
|
|
* array until the caller has WAL-logged this snapshot, and releases the
|
|
* lock. Acquiring ProcArrayLock ensures that no transactions commit until the
|
|
* lock is released.
|
|
*
|
|
* The returned data structure is statically allocated; caller should not
|
|
* modify it, and must not assume it is valid past the next call.
|
|
*
|
|
* This is never executed during recovery so there is no need to look at
|
|
* KnownAssignedXids.
|
|
*
|
|
* Dummy PGPROCs from prepared transaction are included, meaning that this
|
|
* may return entries with duplicated TransactionId values coming from
|
|
* transaction finishing to prepare. Nothing is done about duplicated
|
|
* entries here to not hold on ProcArrayLock more than necessary.
|
|
*
|
|
* We don't worry about updating other counters, we want to keep this as
|
|
* simple as possible and leave GetSnapshotData() as the primary code for
|
|
* that bookkeeping.
|
|
*
|
|
* Note that if any transaction has overflowed its cached subtransactions
|
|
* then there is no real need include any subtransactions.
|
|
*/
|
|
RunningTransactions
|
|
GetRunningTransactionData(void)
|
|
{
|
|
/* result workspace */
|
|
static RunningTransactionsData CurrentRunningXactsData;
|
|
|
|
ProcArrayStruct *arrayP = procArray;
|
|
TransactionId *other_xids = ProcGlobal->xids;
|
|
RunningTransactions CurrentRunningXacts = &CurrentRunningXactsData;
|
|
TransactionId latestCompletedXid;
|
|
TransactionId oldestRunningXid;
|
|
TransactionId *xids;
|
|
int index;
|
|
int count;
|
|
int subcount;
|
|
bool suboverflowed;
|
|
|
|
Assert(!RecoveryInProgress());
|
|
|
|
/*
|
|
* Allocating space for maxProcs xids is usually overkill; numProcs would
|
|
* be sufficient. But it seems better to do the malloc while not holding
|
|
* the lock, so we can't look at numProcs. Likewise, we allocate much
|
|
* more subxip storage than is probably needed.
|
|
*
|
|
* Should only be allocated in bgwriter, since only ever executed during
|
|
* checkpoints.
|
|
*/
|
|
if (CurrentRunningXacts->xids == NULL)
|
|
{
|
|
/*
|
|
* First call
|
|
*/
|
|
CurrentRunningXacts->xids = (TransactionId *)
|
|
malloc(TOTAL_MAX_CACHED_SUBXIDS * sizeof(TransactionId));
|
|
if (CurrentRunningXacts->xids == NULL)
|
|
ereport(ERROR,
|
|
(errcode(ERRCODE_OUT_OF_MEMORY),
|
|
errmsg("out of memory")));
|
|
}
|
|
|
|
xids = CurrentRunningXacts->xids;
|
|
|
|
count = subcount = 0;
|
|
suboverflowed = false;
|
|
|
|
/*
|
|
* Ensure that no xids enter or leave the procarray while we obtain
|
|
* snapshot.
|
|
*/
|
|
LWLockAcquire(ProcArrayLock, LW_SHARED);
|
|
LWLockAcquire(XidGenLock, LW_SHARED);
|
|
|
|
latestCompletedXid =
|
|
XidFromFullTransactionId(ShmemVariableCache->latestCompletedXid);
|
|
oldestRunningXid =
|
|
XidFromFullTransactionId(ShmemVariableCache->nextXid);
|
|
|
|
/*
|
|
* Spin over procArray collecting all xids
|
|
*/
|
|
for (index = 0; index < arrayP->numProcs; index++)
|
|
{
|
|
TransactionId xid;
|
|
|
|
/* Fetch xid just once - see GetNewTransactionId */
|
|
xid = UINT32_ACCESS_ONCE(other_xids[index]);
|
|
|
|
/*
|
|
* We don't need to store transactions that don't have a TransactionId
|
|
* yet because they will not show as running on a standby server.
|
|
*/
|
|
if (!TransactionIdIsValid(xid))
|
|
continue;
|
|
|
|
/*
|
|
* Be careful not to exclude any xids before calculating the values of
|
|
* oldestRunningXid and suboverflowed, since these are used to clean
|
|
* up transaction information held on standbys.
|
|
*/
|
|
if (TransactionIdPrecedes(xid, oldestRunningXid))
|
|
oldestRunningXid = xid;
|
|
|
|
if (ProcGlobal->subxidStates[index].overflowed)
|
|
suboverflowed = true;
|
|
|
|
/*
|
|
* If we wished to exclude xids this would be the right place for it.
|
|
* Procs with the PROC_IN_VACUUM flag set don't usually assign xids,
|
|
* but they do during truncation at the end when they get the lock and
|
|
* truncate, so it is not much of a problem to include them if they
|
|
* are seen and it is cleaner to include them.
|
|
*/
|
|
|
|
xids[count++] = xid;
|
|
}
|
|
|
|
/*
|
|
* Spin over procArray collecting all subxids, but only if there hasn't
|
|
* been a suboverflow.
|
|
*/
|
|
if (!suboverflowed)
|
|
{
|
|
XidCacheStatus *other_subxidstates = ProcGlobal->subxidStates;
|
|
|
|
for (index = 0; index < arrayP->numProcs; index++)
|
|
{
|
|
int pgprocno = arrayP->pgprocnos[index];
|
|
PGPROC *proc = &allProcs[pgprocno];
|
|
int nsubxids;
|
|
|
|
/*
|
|
* Save subtransaction XIDs. Other backends can't add or remove
|
|
* entries while we're holding XidGenLock.
|
|
*/
|
|
nsubxids = other_subxidstates[index].count;
|
|
if (nsubxids > 0)
|
|
{
|
|
/* barrier not really required, as XidGenLock is held, but ... */
|
|
pg_read_barrier(); /* pairs with GetNewTransactionId */
|
|
|
|
memcpy(&xids[count], proc->subxids.xids,
|
|
nsubxids * sizeof(TransactionId));
|
|
count += nsubxids;
|
|
subcount += nsubxids;
|
|
|
|
/*
|
|
* Top-level XID of a transaction is always less than any of
|
|
* its subxids, so we don't need to check if any of the
|
|
* subxids are smaller than oldestRunningXid
|
|
*/
|
|
}
|
|
}
|
|
}
|
|
|
|
/*
|
|
* It's important *not* to include the limits set by slots here because
|
|
* snapbuild.c uses oldestRunningXid to manage its xmin horizon. If those
|
|
* were to be included here the initial value could never increase because
|
|
* of a circular dependency where slots only increase their limits when
|
|
* running xacts increases oldestRunningXid and running xacts only
|
|
* increases if slots do.
|
|
*/
|
|
|
|
CurrentRunningXacts->xcnt = count - subcount;
|
|
CurrentRunningXacts->subxcnt = subcount;
|
|
CurrentRunningXacts->subxid_overflow = suboverflowed;
|
|
CurrentRunningXacts->nextXid = XidFromFullTransactionId(ShmemVariableCache->nextXid);
|
|
CurrentRunningXacts->oldestRunningXid = oldestRunningXid;
|
|
CurrentRunningXacts->latestCompletedXid = latestCompletedXid;
|
|
|
|
Assert(TransactionIdIsValid(CurrentRunningXacts->nextXid));
|
|
Assert(TransactionIdIsValid(CurrentRunningXacts->oldestRunningXid));
|
|
Assert(TransactionIdIsNormal(CurrentRunningXacts->latestCompletedXid));
|
|
|
|
/* We don't release the locks here, the caller is responsible for that */
|
|
|
|
return CurrentRunningXacts;
|
|
}
|
|
|
|
/*
|
|
* GetOldestActiveTransactionId()
|
|
*
|
|
* Similar to GetSnapshotData but returns just oldestActiveXid. We include
|
|
* all PGPROCs with an assigned TransactionId, even VACUUM processes.
|
|
* We look at all databases, though there is no need to include WALSender
|
|
* since this has no effect on hot standby conflicts.
|
|
*
|
|
* This is never executed during recovery so there is no need to look at
|
|
* KnownAssignedXids.
|
|
*
|
|
* We don't worry about updating other counters, we want to keep this as
|
|
* simple as possible and leave GetSnapshotData() as the primary code for
|
|
* that bookkeeping.
|
|
*/
|
|
TransactionId
|
|
GetOldestActiveTransactionId(void)
|
|
{
|
|
ProcArrayStruct *arrayP = procArray;
|
|
TransactionId *other_xids = ProcGlobal->xids;
|
|
TransactionId oldestRunningXid;
|
|
int index;
|
|
|
|
Assert(!RecoveryInProgress());
|
|
|
|
/*
|
|
* Read nextXid, as the upper bound of what's still active.
|
|
*
|
|
* Reading a TransactionId is atomic, but we must grab the lock to make
|
|
* sure that all XIDs < nextXid are already present in the proc array (or
|
|
* have already completed), when we spin over it.
|
|
*/
|
|
LWLockAcquire(XidGenLock, LW_SHARED);
|
|
oldestRunningXid = XidFromFullTransactionId(ShmemVariableCache->nextXid);
|
|
LWLockRelease(XidGenLock);
|
|
|
|
/*
|
|
* Spin over procArray collecting all xids and subxids.
|
|
*/
|
|
LWLockAcquire(ProcArrayLock, LW_SHARED);
|
|
for (index = 0; index < arrayP->numProcs; index++)
|
|
{
|
|
TransactionId xid;
|
|
|
|
/* Fetch xid just once - see GetNewTransactionId */
|
|
xid = UINT32_ACCESS_ONCE(other_xids[index]);
|
|
|
|
if (!TransactionIdIsNormal(xid))
|
|
continue;
|
|
|
|
if (TransactionIdPrecedes(xid, oldestRunningXid))
|
|
oldestRunningXid = xid;
|
|
|
|
/*
|
|
* Top-level XID of a transaction is always less than any of its
|
|
* subxids, so we don't need to check if any of the subxids are
|
|
* smaller than oldestRunningXid
|
|
*/
|
|
}
|
|
LWLockRelease(ProcArrayLock);
|
|
|
|
return oldestRunningXid;
|
|
}
|
|
|
|
/*
|
|
* GetOldestSafeDecodingTransactionId -- lowest xid not affected by vacuum
|
|
*
|
|
* Returns the oldest xid that we can guarantee not to have been affected by
|
|
* vacuum, i.e. no rows >= that xid have been vacuumed away unless the
|
|
* transaction aborted. Note that the value can (and most of the time will) be
|
|
* much more conservative than what really has been affected by vacuum, but we
|
|
* currently don't have better data available.
|
|
*
|
|
* This is useful to initialize the cutoff xid after which a new changeset
|
|
* extraction replication slot can start decoding changes.
|
|
*
|
|
* Must be called with ProcArrayLock held either shared or exclusively,
|
|
* although most callers will want to use exclusive mode since it is expected
|
|
* that the caller will immediately use the xid to peg the xmin horizon.
|
|
*/
|
|
TransactionId
|
|
GetOldestSafeDecodingTransactionId(bool catalogOnly)
|
|
{
|
|
ProcArrayStruct *arrayP = procArray;
|
|
TransactionId oldestSafeXid;
|
|
int index;
|
|
bool recovery_in_progress = RecoveryInProgress();
|
|
|
|
Assert(LWLockHeldByMe(ProcArrayLock));
|
|
|
|
/*
|
|
* Acquire XidGenLock, so no transactions can acquire an xid while we're
|
|
* running. If no transaction with xid were running concurrently a new xid
|
|
* could influence the RecentXmin et al.
|
|
*
|
|
* We initialize the computation to nextXid since that's guaranteed to be
|
|
* a safe, albeit pessimal, value.
|
|
*/
|
|
LWLockAcquire(XidGenLock, LW_SHARED);
|
|
oldestSafeXid = XidFromFullTransactionId(ShmemVariableCache->nextXid);
|
|
|
|
/*
|
|
* If there's already a slot pegging the xmin horizon, we can start with
|
|
* that value, it's guaranteed to be safe since it's computed by this
|
|
* routine initially and has been enforced since. We can always use the
|
|
* slot's general xmin horizon, but the catalog horizon is only usable
|
|
* when only catalog data is going to be looked at.
|
|
*/
|
|
if (TransactionIdIsValid(procArray->replication_slot_xmin) &&
|
|
TransactionIdPrecedes(procArray->replication_slot_xmin,
|
|
oldestSafeXid))
|
|
oldestSafeXid = procArray->replication_slot_xmin;
|
|
|
|
if (catalogOnly &&
|
|
TransactionIdIsValid(procArray->replication_slot_catalog_xmin) &&
|
|
TransactionIdPrecedes(procArray->replication_slot_catalog_xmin,
|
|
oldestSafeXid))
|
|
oldestSafeXid = procArray->replication_slot_catalog_xmin;
|
|
|
|
/*
|
|
* If we're not in recovery, we walk over the procarray and collect the
|
|
* lowest xid. Since we're called with ProcArrayLock held and have
|
|
* acquired XidGenLock, no entries can vanish concurrently, since
|
|
* ProcGlobal->xids[i] is only set with XidGenLock held and only cleared
|
|
* with ProcArrayLock held.
|
|
*
|
|
* In recovery we can't lower the safe value besides what we've computed
|
|
* above, so we'll have to wait a bit longer there. We unfortunately can
|
|
* *not* use KnownAssignedXidsGetOldestXmin() since the KnownAssignedXids
|
|
* machinery can miss values and return an older value than is safe.
|
|
*/
|
|
if (!recovery_in_progress)
|
|
{
|
|
TransactionId *other_xids = ProcGlobal->xids;
|
|
|
|
/*
|
|
* Spin over procArray collecting min(ProcGlobal->xids[i])
|
|
*/
|
|
for (index = 0; index < arrayP->numProcs; index++)
|
|
{
|
|
TransactionId xid;
|
|
|
|
/* Fetch xid just once - see GetNewTransactionId */
|
|
xid = UINT32_ACCESS_ONCE(other_xids[index]);
|
|
|
|
if (!TransactionIdIsNormal(xid))
|
|
continue;
|
|
|
|
if (TransactionIdPrecedes(xid, oldestSafeXid))
|
|
oldestSafeXid = xid;
|
|
}
|
|
}
|
|
|
|
LWLockRelease(XidGenLock);
|
|
|
|
return oldestSafeXid;
|
|
}
|
|
|
|
/*
|
|
* GetVirtualXIDsDelayingChkpt -- Get the VXIDs of transactions that are
|
|
* delaying checkpoint because they have critical actions in progress.
|
|
*
|
|
* Constructs an array of VXIDs of transactions that are currently in commit
|
|
* critical sections, as shown by having specified delayChkptFlags bits set
|
|
* in their PGPROC.
|
|
*
|
|
* Returns a palloc'd array that should be freed by the caller.
|
|
* *nvxids is the number of valid entries.
|
|
*
|
|
* Note that because backends set or clear delayChkptFlags without holding any
|
|
* lock, the result is somewhat indeterminate, but we don't really care. Even
|
|
* in a multiprocessor with delayed writes to shared memory, it should be
|
|
* certain that setting of delayChkptFlags will propagate to shared memory
|
|
* when the backend takes a lock, so we cannot fail to see a virtual xact as
|
|
* delayChkptFlags if it's already inserted its commit record. Whether it
|
|
* takes a little while for clearing of delayChkptFlags to propagate is
|
|
* unimportant for correctness.
|
|
*/
|
|
VirtualTransactionId *
|
|
GetVirtualXIDsDelayingChkpt(int *nvxids, int type)
|
|
{
|
|
VirtualTransactionId *vxids;
|
|
ProcArrayStruct *arrayP = procArray;
|
|
int count = 0;
|
|
int index;
|
|
|
|
Assert(type != 0);
|
|
|
|
/* allocate what's certainly enough result space */
|
|
vxids = (VirtualTransactionId *)
|
|
palloc(sizeof(VirtualTransactionId) * arrayP->maxProcs);
|
|
|
|
LWLockAcquire(ProcArrayLock, LW_SHARED);
|
|
|
|
for (index = 0; index < arrayP->numProcs; index++)
|
|
{
|
|
int pgprocno = arrayP->pgprocnos[index];
|
|
PGPROC *proc = &allProcs[pgprocno];
|
|
|
|
if ((proc->delayChkptFlags & type) != 0)
|
|
{
|
|
VirtualTransactionId vxid;
|
|
|
|
GET_VXID_FROM_PGPROC(vxid, *proc);
|
|
if (VirtualTransactionIdIsValid(vxid))
|
|
vxids[count++] = vxid;
|
|
}
|
|
}
|
|
|
|
LWLockRelease(ProcArrayLock);
|
|
|
|
*nvxids = count;
|
|
return vxids;
|
|
}
|
|
|
|
/*
|
|
* HaveVirtualXIDsDelayingChkpt -- Are any of the specified VXIDs delaying?
|
|
*
|
|
* This is used with the results of GetVirtualXIDsDelayingChkpt to see if any
|
|
* of the specified VXIDs are still in critical sections of code.
|
|
*
|
|
* Note: this is O(N^2) in the number of vxacts that are/were delaying, but
|
|
* those numbers should be small enough for it not to be a problem.
|
|
*/
|
|
bool
|
|
HaveVirtualXIDsDelayingChkpt(VirtualTransactionId *vxids, int nvxids, int type)
|
|
{
|
|
bool result = false;
|
|
ProcArrayStruct *arrayP = procArray;
|
|
int index;
|
|
|
|
Assert(type != 0);
|
|
|
|
LWLockAcquire(ProcArrayLock, LW_SHARED);
|
|
|
|
for (index = 0; index < arrayP->numProcs; index++)
|
|
{
|
|
int pgprocno = arrayP->pgprocnos[index];
|
|
PGPROC *proc = &allProcs[pgprocno];
|
|
VirtualTransactionId vxid;
|
|
|
|
GET_VXID_FROM_PGPROC(vxid, *proc);
|
|
|
|
if ((proc->delayChkptFlags & type) != 0 &&
|
|
VirtualTransactionIdIsValid(vxid))
|
|
{
|
|
int i;
|
|
|
|
for (i = 0; i < nvxids; i++)
|
|
{
|
|
if (VirtualTransactionIdEquals(vxid, vxids[i]))
|
|
{
|
|
result = true;
|
|
break;
|
|
}
|
|
}
|
|
if (result)
|
|
break;
|
|
}
|
|
}
|
|
|
|
LWLockRelease(ProcArrayLock);
|
|
|
|
return result;
|
|
}
|
|
|
|
/*
|
|
* BackendPidGetProc -- get a backend's PGPROC given its PID
|
|
*
|
|
* Returns NULL if not found. Note that it is up to the caller to be
|
|
* sure that the question remains meaningful for long enough for the
|
|
* answer to be used ...
|
|
*/
|
|
PGPROC *
|
|
BackendPidGetProc(int pid)
|
|
{
|
|
PGPROC *result;
|
|
|
|
if (pid == 0) /* never match dummy PGPROCs */
|
|
return NULL;
|
|
|
|
LWLockAcquire(ProcArrayLock, LW_SHARED);
|
|
|
|
result = BackendPidGetProcWithLock(pid);
|
|
|
|
LWLockRelease(ProcArrayLock);
|
|
|
|
return result;
|
|
}
|
|
|
|
/*
|
|
* BackendPidGetProcWithLock -- get a backend's PGPROC given its PID
|
|
*
|
|
* Same as above, except caller must be holding ProcArrayLock. The found
|
|
* entry, if any, can be assumed to be valid as long as the lock remains held.
|
|
*/
|
|
PGPROC *
|
|
BackendPidGetProcWithLock(int pid)
|
|
{
|
|
PGPROC *result = NULL;
|
|
ProcArrayStruct *arrayP = procArray;
|
|
int index;
|
|
|
|
if (pid == 0) /* never match dummy PGPROCs */
|
|
return NULL;
|
|
|
|
for (index = 0; index < arrayP->numProcs; index++)
|
|
{
|
|
PGPROC *proc = &allProcs[arrayP->pgprocnos[index]];
|
|
|
|
if (proc->pid == pid)
|
|
{
|
|
result = proc;
|
|
break;
|
|
}
|
|
}
|
|
|
|
return result;
|
|
}
|
|
|
|
/*
|
|
* BackendXidGetPid -- get a backend's pid given its XID
|
|
*
|
|
* Returns 0 if not found or it's a prepared transaction. Note that
|
|
* it is up to the caller to be sure that the question remains
|
|
* meaningful for long enough for the answer to be used ...
|
|
*
|
|
* Only main transaction Ids are considered. This function is mainly
|
|
* useful for determining what backend owns a lock.
|
|
*
|
|
* Beware that not every xact has an XID assigned. However, as long as you
|
|
* only call this using an XID found on disk, you're safe.
|
|
*/
|
|
int
|
|
BackendXidGetPid(TransactionId xid)
|
|
{
|
|
int result = 0;
|
|
ProcArrayStruct *arrayP = procArray;
|
|
TransactionId *other_xids = ProcGlobal->xids;
|
|
int index;
|
|
|
|
if (xid == InvalidTransactionId) /* never match invalid xid */
|
|
return 0;
|
|
|
|
LWLockAcquire(ProcArrayLock, LW_SHARED);
|
|
|
|
for (index = 0; index < arrayP->numProcs; index++)
|
|
{
|
|
int pgprocno = arrayP->pgprocnos[index];
|
|
PGPROC *proc = &allProcs[pgprocno];
|
|
|
|
if (other_xids[index] == xid)
|
|
{
|
|
result = proc->pid;
|
|
break;
|
|
}
|
|
}
|
|
|
|
LWLockRelease(ProcArrayLock);
|
|
|
|
return result;
|
|
}
|
|
|
|
/*
|
|
* IsBackendPid -- is a given pid a running backend
|
|
*
|
|
* This is not called by the backend, but is called by external modules.
|
|
*/
|
|
bool
|
|
IsBackendPid(int pid)
|
|
{
|
|
return (BackendPidGetProc(pid) != NULL);
|
|
}
|
|
|
|
|
|
/*
|
|
* GetCurrentVirtualXIDs -- returns an array of currently active VXIDs.
|
|
*
|
|
* The array is palloc'd. The number of valid entries is returned into *nvxids.
|
|
*
|
|
* The arguments allow filtering the set of VXIDs returned. Our own process
|
|
* is always skipped. In addition:
|
|
* If limitXmin is not InvalidTransactionId, skip processes with
|
|
* xmin > limitXmin.
|
|
* If excludeXmin0 is true, skip processes with xmin = 0.
|
|
* If allDbs is false, skip processes attached to other databases.
|
|
* If excludeVacuum isn't zero, skip processes for which
|
|
* (statusFlags & excludeVacuum) is not zero.
|
|
*
|
|
* Note: the purpose of the limitXmin and excludeXmin0 parameters is to
|
|
* allow skipping backends whose oldest live snapshot is no older than
|
|
* some snapshot we have. Since we examine the procarray with only shared
|
|
* lock, there are race conditions: a backend could set its xmin just after
|
|
* we look. Indeed, on multiprocessors with weak memory ordering, the
|
|
* other backend could have set its xmin *before* we look. We know however
|
|
* that such a backend must have held shared ProcArrayLock overlapping our
|
|
* own hold of ProcArrayLock, else we would see its xmin update. Therefore,
|
|
* any snapshot the other backend is taking concurrently with our scan cannot
|
|
* consider any transactions as still running that we think are committed
|
|
* (since backends must hold ProcArrayLock exclusive to commit).
|
|
*/
|
|
VirtualTransactionId *
|
|
GetCurrentVirtualXIDs(TransactionId limitXmin, bool excludeXmin0,
|
|
bool allDbs, int excludeVacuum,
|
|
int *nvxids)
|
|
{
|
|
VirtualTransactionId *vxids;
|
|
ProcArrayStruct *arrayP = procArray;
|
|
int count = 0;
|
|
int index;
|
|
|
|
/* allocate what's certainly enough result space */
|
|
vxids = (VirtualTransactionId *)
|
|
palloc(sizeof(VirtualTransactionId) * arrayP->maxProcs);
|
|
|
|
LWLockAcquire(ProcArrayLock, LW_SHARED);
|
|
|
|
for (index = 0; index < arrayP->numProcs; index++)
|
|
{
|
|
int pgprocno = arrayP->pgprocnos[index];
|
|
PGPROC *proc = &allProcs[pgprocno];
|
|
uint8 statusFlags = ProcGlobal->statusFlags[index];
|
|
|
|
if (proc == MyProc)
|
|
continue;
|
|
|
|
if (excludeVacuum & statusFlags)
|
|
continue;
|
|
|
|
if (allDbs || proc->databaseId == MyDatabaseId)
|
|
{
|
|
/* Fetch xmin just once - might change on us */
|
|
TransactionId pxmin = UINT32_ACCESS_ONCE(proc->xmin);
|
|
|
|
if (excludeXmin0 && !TransactionIdIsValid(pxmin))
|
|
continue;
|
|
|
|
/*
|
|
* InvalidTransactionId precedes all other XIDs, so a proc that
|
|
* hasn't set xmin yet will not be rejected by this test.
|
|
*/
|
|
if (!TransactionIdIsValid(limitXmin) ||
|
|
TransactionIdPrecedesOrEquals(pxmin, limitXmin))
|
|
{
|
|
VirtualTransactionId vxid;
|
|
|
|
GET_VXID_FROM_PGPROC(vxid, *proc);
|
|
if (VirtualTransactionIdIsValid(vxid))
|
|
vxids[count++] = vxid;
|
|
}
|
|
}
|
|
}
|
|
|
|
LWLockRelease(ProcArrayLock);
|
|
|
|
*nvxids = count;
|
|
return vxids;
|
|
}
|
|
|
|
/*
|
|
* GetConflictingVirtualXIDs -- returns an array of currently active VXIDs.
|
|
*
|
|
* Usage is limited to conflict resolution during recovery on standby servers.
|
|
* limitXmin is supplied as either a cutoff with snapshotConflictHorizon
|
|
* semantics, or InvalidTransactionId in cases where caller cannot accurately
|
|
* determine a safe snapshotConflictHorizon value.
|
|
*
|
|
* If limitXmin is InvalidTransactionId then we want to kill everybody,
|
|
* so we're not worried if they have a snapshot or not, nor does it really
|
|
* matter what type of lock we hold. Caller must avoid calling here with
|
|
* snapshotConflictHorizon style cutoffs that were set to InvalidTransactionId
|
|
* during original execution, since that actually indicates that there is
|
|
* definitely no need for a recovery conflict (the snapshotConflictHorizon
|
|
* convention for InvalidTransactionId values is the opposite of our own!).
|
|
*
|
|
* All callers that are checking xmins always now supply a valid and useful
|
|
* value for limitXmin. The limitXmin is always lower than the lowest
|
|
* numbered KnownAssignedXid that is not already a FATAL error. This is
|
|
* because we only care about cleanup records that are cleaning up tuple
|
|
* versions from committed transactions. In that case they will only occur
|
|
* at the point where the record is less than the lowest running xid. That
|
|
* allows us to say that if any backend takes a snapshot concurrently with
|
|
* us then the conflict assessment made here would never include the snapshot
|
|
* that is being derived. So we take LW_SHARED on the ProcArray and allow
|
|
* concurrent snapshots when limitXmin is valid. We might think about adding
|
|
* Assert(limitXmin < lowest(KnownAssignedXids))
|
|
* but that would not be true in the case of FATAL errors lagging in array,
|
|
* but we already know those are bogus anyway, so we skip that test.
|
|
*
|
|
* If dbOid is valid we skip backends attached to other databases.
|
|
*
|
|
* Be careful to *not* pfree the result from this function. We reuse
|
|
* this array sufficiently often that we use malloc for the result.
|
|
*/
|
|
VirtualTransactionId *
|
|
GetConflictingVirtualXIDs(TransactionId limitXmin, Oid dbOid)
|
|
{
|
|
static VirtualTransactionId *vxids;
|
|
ProcArrayStruct *arrayP = procArray;
|
|
int count = 0;
|
|
int index;
|
|
|
|
/*
|
|
* If first time through, get workspace to remember main XIDs in. We
|
|
* malloc it permanently to avoid repeated palloc/pfree overhead. Allow
|
|
* result space, remembering room for a terminator.
|
|
*/
|
|
if (vxids == NULL)
|
|
{
|
|
vxids = (VirtualTransactionId *)
|
|
malloc(sizeof(VirtualTransactionId) * (arrayP->maxProcs + 1));
|
|
if (vxids == NULL)
|
|
ereport(ERROR,
|
|
(errcode(ERRCODE_OUT_OF_MEMORY),
|
|
errmsg("out of memory")));
|
|
}
|
|
|
|
LWLockAcquire(ProcArrayLock, LW_SHARED);
|
|
|
|
for (index = 0; index < arrayP->numProcs; index++)
|
|
{
|
|
int pgprocno = arrayP->pgprocnos[index];
|
|
PGPROC *proc = &allProcs[pgprocno];
|
|
|
|
/* Exclude prepared transactions */
|
|
if (proc->pid == 0)
|
|
continue;
|
|
|
|
if (!OidIsValid(dbOid) ||
|
|
proc->databaseId == dbOid)
|
|
{
|
|
/* Fetch xmin just once - can't change on us, but good coding */
|
|
TransactionId pxmin = UINT32_ACCESS_ONCE(proc->xmin);
|
|
|
|
/*
|
|
* We ignore an invalid pxmin because this means that backend has
|
|
* no snapshot currently. We hold a Share lock to avoid contention
|
|
* with users taking snapshots. That is not a problem because the
|
|
* current xmin is always at least one higher than the latest
|
|
* removed xid, so any new snapshot would never conflict with the
|
|
* test here.
|
|
*/
|
|
if (!TransactionIdIsValid(limitXmin) ||
|
|
(TransactionIdIsValid(pxmin) && !TransactionIdFollows(pxmin, limitXmin)))
|
|
{
|
|
VirtualTransactionId vxid;
|
|
|
|
GET_VXID_FROM_PGPROC(vxid, *proc);
|
|
if (VirtualTransactionIdIsValid(vxid))
|
|
vxids[count++] = vxid;
|
|
}
|
|
}
|
|
}
|
|
|
|
LWLockRelease(ProcArrayLock);
|
|
|
|
/* add the terminator */
|
|
vxids[count].backendId = InvalidBackendId;
|
|
vxids[count].localTransactionId = InvalidLocalTransactionId;
|
|
|
|
return vxids;
|
|
}
|
|
|
|
/*
|
|
* CancelVirtualTransaction - used in recovery conflict processing
|
|
*
|
|
* Returns pid of the process signaled, or 0 if not found.
|
|
*/
|
|
pid_t
|
|
CancelVirtualTransaction(VirtualTransactionId vxid, ProcSignalReason sigmode)
|
|
{
|
|
return SignalVirtualTransaction(vxid, sigmode, true);
|
|
}
|
|
|
|
pid_t
|
|
SignalVirtualTransaction(VirtualTransactionId vxid, ProcSignalReason sigmode,
|
|
bool conflictPending)
|
|
{
|
|
ProcArrayStruct *arrayP = procArray;
|
|
int index;
|
|
pid_t pid = 0;
|
|
|
|
LWLockAcquire(ProcArrayLock, LW_SHARED);
|
|
|
|
for (index = 0; index < arrayP->numProcs; index++)
|
|
{
|
|
int pgprocno = arrayP->pgprocnos[index];
|
|
PGPROC *proc = &allProcs[pgprocno];
|
|
VirtualTransactionId procvxid;
|
|
|
|
GET_VXID_FROM_PGPROC(procvxid, *proc);
|
|
|
|
if (procvxid.backendId == vxid.backendId &&
|
|
procvxid.localTransactionId == vxid.localTransactionId)
|
|
{
|
|
proc->recoveryConflictPending = conflictPending;
|
|
pid = proc->pid;
|
|
if (pid != 0)
|
|
{
|
|
/*
|
|
* Kill the pid if it's still here. If not, that's what we
|
|
* wanted so ignore any errors.
|
|
*/
|
|
(void) SendProcSignal(pid, sigmode, vxid.backendId);
|
|
}
|
|
break;
|
|
}
|
|
}
|
|
|
|
LWLockRelease(ProcArrayLock);
|
|
|
|
return pid;
|
|
}
|
|
|
|
/*
|
|
* MinimumActiveBackends --- count backends (other than myself) that are
|
|
* in active transactions. Return true if the count exceeds the
|
|
* minimum threshold passed. This is used as a heuristic to decide if
|
|
* a pre-XLOG-flush delay is worthwhile during commit.
|
|
*
|
|
* Do not count backends that are blocked waiting for locks, since they are
|
|
* not going to get to run until someone else commits.
|
|
*/
|
|
bool
|
|
MinimumActiveBackends(int min)
|
|
{
|
|
ProcArrayStruct *arrayP = procArray;
|
|
int count = 0;
|
|
int index;
|
|
|
|
/* Quick short-circuit if no minimum is specified */
|
|
if (min == 0)
|
|
return true;
|
|
|
|
/*
|
|
* Note: for speed, we don't acquire ProcArrayLock. This is a little bit
|
|
* bogus, but since we are only testing fields for zero or nonzero, it
|
|
* should be OK. The result is only used for heuristic purposes anyway...
|
|
*/
|
|
for (index = 0; index < arrayP->numProcs; index++)
|
|
{
|
|
int pgprocno = arrayP->pgprocnos[index];
|
|
PGPROC *proc = &allProcs[pgprocno];
|
|
|
|
/*
|
|
* Since we're not holding a lock, need to be prepared to deal with
|
|
* garbage, as someone could have incremented numProcs but not yet
|
|
* filled the structure.
|
|
*
|
|
* If someone just decremented numProcs, 'proc' could also point to a
|
|
* PGPROC entry that's no longer in the array. It still points to a
|
|
* PGPROC struct, though, because freed PGPROC entries just go to the
|
|
* free list and are recycled. Its contents are nonsense in that case,
|
|
* but that's acceptable for this function.
|
|
*/
|
|
if (pgprocno == -1)
|
|
continue; /* do not count deleted entries */
|
|
if (proc == MyProc)
|
|
continue; /* do not count myself */
|
|
if (proc->xid == InvalidTransactionId)
|
|
continue; /* do not count if no XID assigned */
|
|
if (proc->pid == 0)
|
|
continue; /* do not count prepared xacts */
|
|
if (proc->waitLock != NULL)
|
|
continue; /* do not count if blocked on a lock */
|
|
count++;
|
|
if (count >= min)
|
|
break;
|
|
}
|
|
|
|
return count >= min;
|
|
}
|
|
|
|
/*
|
|
* CountDBBackends --- count backends that are using specified database
|
|
*/
|
|
int
|
|
CountDBBackends(Oid databaseid)
|
|
{
|
|
ProcArrayStruct *arrayP = procArray;
|
|
int count = 0;
|
|
int index;
|
|
|
|
LWLockAcquire(ProcArrayLock, LW_SHARED);
|
|
|
|
for (index = 0; index < arrayP->numProcs; index++)
|
|
{
|
|
int pgprocno = arrayP->pgprocnos[index];
|
|
PGPROC *proc = &allProcs[pgprocno];
|
|
|
|
if (proc->pid == 0)
|
|
continue; /* do not count prepared xacts */
|
|
if (!OidIsValid(databaseid) ||
|
|
proc->databaseId == databaseid)
|
|
count++;
|
|
}
|
|
|
|
LWLockRelease(ProcArrayLock);
|
|
|
|
return count;
|
|
}
|
|
|
|
/*
|
|
* CountDBConnections --- counts database backends ignoring any background
|
|
* worker processes
|
|
*/
|
|
int
|
|
CountDBConnections(Oid databaseid)
|
|
{
|
|
ProcArrayStruct *arrayP = procArray;
|
|
int count = 0;
|
|
int index;
|
|
|
|
LWLockAcquire(ProcArrayLock, LW_SHARED);
|
|
|
|
for (index = 0; index < arrayP->numProcs; index++)
|
|
{
|
|
int pgprocno = arrayP->pgprocnos[index];
|
|
PGPROC *proc = &allProcs[pgprocno];
|
|
|
|
if (proc->pid == 0)
|
|
continue; /* do not count prepared xacts */
|
|
if (proc->isBackgroundWorker)
|
|
continue; /* do not count background workers */
|
|
if (!OidIsValid(databaseid) ||
|
|
proc->databaseId == databaseid)
|
|
count++;
|
|
}
|
|
|
|
LWLockRelease(ProcArrayLock);
|
|
|
|
return count;
|
|
}
|
|
|
|
/*
|
|
* CancelDBBackends --- cancel backends that are using specified database
|
|
*/
|
|
void
|
|
CancelDBBackends(Oid databaseid, ProcSignalReason sigmode, bool conflictPending)
|
|
{
|
|
ProcArrayStruct *arrayP = procArray;
|
|
int index;
|
|
|
|
/* tell all backends to die */
|
|
LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
|
|
|
|
for (index = 0; index < arrayP->numProcs; index++)
|
|
{
|
|
int pgprocno = arrayP->pgprocnos[index];
|
|
PGPROC *proc = &allProcs[pgprocno];
|
|
|
|
if (databaseid == InvalidOid || proc->databaseId == databaseid)
|
|
{
|
|
VirtualTransactionId procvxid;
|
|
pid_t pid;
|
|
|
|
GET_VXID_FROM_PGPROC(procvxid, *proc);
|
|
|
|
proc->recoveryConflictPending = conflictPending;
|
|
pid = proc->pid;
|
|
if (pid != 0)
|
|
{
|
|
/*
|
|
* Kill the pid if it's still here. If not, that's what we
|
|
* wanted so ignore any errors.
|
|
*/
|
|
(void) SendProcSignal(pid, sigmode, procvxid.backendId);
|
|
}
|
|
}
|
|
}
|
|
|
|
LWLockRelease(ProcArrayLock);
|
|
}
|
|
|
|
/*
|
|
* CountUserBackends --- count backends that are used by specified user
|
|
*/
|
|
int
|
|
CountUserBackends(Oid roleid)
|
|
{
|
|
ProcArrayStruct *arrayP = procArray;
|
|
int count = 0;
|
|
int index;
|
|
|
|
LWLockAcquire(ProcArrayLock, LW_SHARED);
|
|
|
|
for (index = 0; index < arrayP->numProcs; index++)
|
|
{
|
|
int pgprocno = arrayP->pgprocnos[index];
|
|
PGPROC *proc = &allProcs[pgprocno];
|
|
|
|
if (proc->pid == 0)
|
|
continue; /* do not count prepared xacts */
|
|
if (proc->isBackgroundWorker)
|
|
continue; /* do not count background workers */
|
|
if (proc->roleId == roleid)
|
|
count++;
|
|
}
|
|
|
|
LWLockRelease(ProcArrayLock);
|
|
|
|
return count;
|
|
}
|
|
|
|
/*
|
|
* CountOtherDBBackends -- check for other backends running in the given DB
|
|
*
|
|
* If there are other backends in the DB, we will wait a maximum of 5 seconds
|
|
* for them to exit. Autovacuum backends are encouraged to exit early by
|
|
* sending them SIGTERM, but normal user backends are just waited for.
|
|
*
|
|
* The current backend is always ignored; it is caller's responsibility to
|
|
* check whether the current backend uses the given DB, if it's important.
|
|
*
|
|
* Returns true if there are (still) other backends in the DB, false if not.
|
|
* Also, *nbackends and *nprepared are set to the number of other backends
|
|
* and prepared transactions in the DB, respectively.
|
|
*
|
|
* This function is used to interlock DROP DATABASE and related commands
|
|
* against there being any active backends in the target DB --- dropping the
|
|
* DB while active backends remain would be a Bad Thing. Note that we cannot
|
|
* detect here the possibility of a newly-started backend that is trying to
|
|
* connect to the doomed database, so additional interlocking is needed during
|
|
* backend startup. The caller should normally hold an exclusive lock on the
|
|
* target DB before calling this, which is one reason we mustn't wait
|
|
* indefinitely.
|
|
*/
|
|
bool
|
|
CountOtherDBBackends(Oid databaseId, int *nbackends, int *nprepared)
|
|
{
|
|
ProcArrayStruct *arrayP = procArray;
|
|
|
|
#define MAXAUTOVACPIDS 10 /* max autovacs to SIGTERM per iteration */
|
|
int autovac_pids[MAXAUTOVACPIDS];
|
|
int tries;
|
|
|
|
/* 50 tries with 100ms sleep between tries makes 5 sec total wait */
|
|
for (tries = 0; tries < 50; tries++)
|
|
{
|
|
int nautovacs = 0;
|
|
bool found = false;
|
|
int index;
|
|
|
|
CHECK_FOR_INTERRUPTS();
|
|
|
|
*nbackends = *nprepared = 0;
|
|
|
|
LWLockAcquire(ProcArrayLock, LW_SHARED);
|
|
|
|
for (index = 0; index < arrayP->numProcs; index++)
|
|
{
|
|
int pgprocno = arrayP->pgprocnos[index];
|
|
PGPROC *proc = &allProcs[pgprocno];
|
|
uint8 statusFlags = ProcGlobal->statusFlags[index];
|
|
|
|
if (proc->databaseId != databaseId)
|
|
continue;
|
|
if (proc == MyProc)
|
|
continue;
|
|
|
|
found = true;
|
|
|
|
if (proc->pid == 0)
|
|
(*nprepared)++;
|
|
else
|
|
{
|
|
(*nbackends)++;
|
|
if ((statusFlags & PROC_IS_AUTOVACUUM) &&
|
|
nautovacs < MAXAUTOVACPIDS)
|
|
autovac_pids[nautovacs++] = proc->pid;
|
|
}
|
|
}
|
|
|
|
LWLockRelease(ProcArrayLock);
|
|
|
|
if (!found)
|
|
return false; /* no conflicting backends, so done */
|
|
|
|
/*
|
|
* Send SIGTERM to any conflicting autovacuums before sleeping. We
|
|
* postpone this step until after the loop because we don't want to
|
|
* hold ProcArrayLock while issuing kill(). We have no idea what might
|
|
* block kill() inside the kernel...
|
|
*/
|
|
for (index = 0; index < nautovacs; index++)
|
|
(void) kill(autovac_pids[index], SIGTERM); /* ignore any error */
|
|
|
|
/* sleep, then try again */
|
|
pg_usleep(100 * 1000L); /* 100ms */
|
|
}
|
|
|
|
return true; /* timed out, still conflicts */
|
|
}
|
|
|
|
/*
|
|
* Terminate existing connections to the specified database. This routine
|
|
* is used by the DROP DATABASE command when user has asked to forcefully
|
|
* drop the database.
|
|
*
|
|
* The current backend is always ignored; it is caller's responsibility to
|
|
* check whether the current backend uses the given DB, if it's important.
|
|
*
|
|
* It doesn't allow to terminate the connections even if there is a one
|
|
* backend with the prepared transaction in the target database.
|
|
*/
|
|
void
|
|
TerminateOtherDBBackends(Oid databaseId)
|
|
{
|
|
ProcArrayStruct *arrayP = procArray;
|
|
List *pids = NIL;
|
|
int nprepared = 0;
|
|
int i;
|
|
|
|
LWLockAcquire(ProcArrayLock, LW_SHARED);
|
|
|
|
for (i = 0; i < procArray->numProcs; i++)
|
|
{
|
|
int pgprocno = arrayP->pgprocnos[i];
|
|
PGPROC *proc = &allProcs[pgprocno];
|
|
|
|
if (proc->databaseId != databaseId)
|
|
continue;
|
|
if (proc == MyProc)
|
|
continue;
|
|
|
|
if (proc->pid != 0)
|
|
pids = lappend_int(pids, proc->pid);
|
|
else
|
|
nprepared++;
|
|
}
|
|
|
|
LWLockRelease(ProcArrayLock);
|
|
|
|
if (nprepared > 0)
|
|
ereport(ERROR,
|
|
(errcode(ERRCODE_OBJECT_IN_USE),
|
|
errmsg("database \"%s\" is being used by prepared transactions",
|
|
get_database_name(databaseId)),
|
|
errdetail_plural("There is %d prepared transaction using the database.",
|
|
"There are %d prepared transactions using the database.",
|
|
nprepared,
|
|
nprepared)));
|
|
|
|
if (pids)
|
|
{
|
|
ListCell *lc;
|
|
|
|
/*
|
|
* Check whether we have the necessary rights to terminate other
|
|
* sessions. We don't terminate any session until we ensure that we
|
|
* have rights on all the sessions to be terminated. These checks are
|
|
* the same as we do in pg_terminate_backend.
|
|
*
|
|
* In this case we don't raise some warnings - like "PID %d is not a
|
|
* PostgreSQL server process", because for us already finished session
|
|
* is not a problem.
|
|
*/
|
|
foreach(lc, pids)
|
|
{
|
|
int pid = lfirst_int(lc);
|
|
PGPROC *proc = BackendPidGetProc(pid);
|
|
|
|
if (proc != NULL)
|
|
{
|
|
/* Only allow superusers to signal superuser-owned backends. */
|
|
if (superuser_arg(proc->roleId) && !superuser())
|
|
ereport(ERROR,
|
|
(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
|
|
errmsg("must be a superuser to terminate superuser process")));
|
|
|
|
/* Users can signal backends they have role membership in. */
|
|
if (!has_privs_of_role(GetUserId(), proc->roleId) &&
|
|
!has_privs_of_role(GetUserId(), ROLE_PG_SIGNAL_BACKEND))
|
|
ereport(ERROR,
|
|
(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
|
|
errmsg("permission denied to terminate process"),
|
|
errdetail("Only roles with privileges of the role whose process is being terminated or with privileges of the \"%s\" role may terminate this process.",
|
|
"pg_signal_backend")));
|
|
}
|
|
}
|
|
|
|
/*
|
|
* There's a race condition here: once we release the ProcArrayLock,
|
|
* it's possible for the session to exit before we issue kill. That
|
|
* race condition possibility seems too unlikely to worry about. See
|
|
* pg_signal_backend.
|
|
*/
|
|
foreach(lc, pids)
|
|
{
|
|
int pid = lfirst_int(lc);
|
|
PGPROC *proc = BackendPidGetProc(pid);
|
|
|
|
if (proc != NULL)
|
|
{
|
|
/*
|
|
* If we have setsid(), signal the backend's whole process
|
|
* group
|
|
*/
|
|
#ifdef HAVE_SETSID
|
|
(void) kill(-pid, SIGTERM);
|
|
#else
|
|
(void) kill(pid, SIGTERM);
|
|
#endif
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
/*
|
|
* ProcArraySetReplicationSlotXmin
|
|
*
|
|
* Install limits to future computations of the xmin horizon to prevent vacuum
|
|
* and HOT pruning from removing affected rows still needed by clients with
|
|
* replication slots.
|
|
*/
|
|
void
|
|
ProcArraySetReplicationSlotXmin(TransactionId xmin, TransactionId catalog_xmin,
|
|
bool already_locked)
|
|
{
|
|
Assert(!already_locked || LWLockHeldByMe(ProcArrayLock));
|
|
|
|
if (!already_locked)
|
|
LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
|
|
|
|
procArray->replication_slot_xmin = xmin;
|
|
procArray->replication_slot_catalog_xmin = catalog_xmin;
|
|
|
|
if (!already_locked)
|
|
LWLockRelease(ProcArrayLock);
|
|
|
|
elog(DEBUG1, "xmin required by slots: data %u, catalog %u",
|
|
xmin, catalog_xmin);
|
|
}
|
|
|
|
/*
|
|
* ProcArrayGetReplicationSlotXmin
|
|
*
|
|
* Return the current slot xmin limits. That's useful to be able to remove
|
|
* data that's older than those limits.
|
|
*/
|
|
void
|
|
ProcArrayGetReplicationSlotXmin(TransactionId *xmin,
|
|
TransactionId *catalog_xmin)
|
|
{
|
|
LWLockAcquire(ProcArrayLock, LW_SHARED);
|
|
|
|
if (xmin != NULL)
|
|
*xmin = procArray->replication_slot_xmin;
|
|
|
|
if (catalog_xmin != NULL)
|
|
*catalog_xmin = procArray->replication_slot_catalog_xmin;
|
|
|
|
LWLockRelease(ProcArrayLock);
|
|
}
|
|
|
|
/*
|
|
* XidCacheRemoveRunningXids
|
|
*
|
|
* Remove a bunch of TransactionIds from the list of known-running
|
|
* subtransactions for my backend. Both the specified xid and those in
|
|
* the xids[] array (of length nxids) are removed from the subxids cache.
|
|
* latestXid must be the latest XID among the group.
|
|
*/
|
|
void
|
|
XidCacheRemoveRunningXids(TransactionId xid,
|
|
int nxids, const TransactionId *xids,
|
|
TransactionId latestXid)
|
|
{
|
|
int i,
|
|
j;
|
|
XidCacheStatus *mysubxidstat;
|
|
|
|
Assert(TransactionIdIsValid(xid));
|
|
|
|
/*
|
|
* We must hold ProcArrayLock exclusively in order to remove transactions
|
|
* from the PGPROC array. (See src/backend/access/transam/README.) It's
|
|
* possible this could be relaxed since we know this routine is only used
|
|
* to abort subtransactions, but pending closer analysis we'd best be
|
|
* conservative.
|
|
*
|
|
* Note that we do not have to be careful about memory ordering of our own
|
|
* reads wrt. GetNewTransactionId() here - only this process can modify
|
|
* relevant fields of MyProc/ProcGlobal->xids[]. But we do have to be
|
|
* careful about our own writes being well ordered.
|
|
*/
|
|
LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
|
|
|
|
mysubxidstat = &ProcGlobal->subxidStates[MyProc->pgxactoff];
|
|
|
|
/*
|
|
* Under normal circumstances xid and xids[] will be in increasing order,
|
|
* as will be the entries in subxids. Scan backwards to avoid O(N^2)
|
|
* behavior when removing a lot of xids.
|
|
*/
|
|
for (i = nxids - 1; i >= 0; i--)
|
|
{
|
|
TransactionId anxid = xids[i];
|
|
|
|
for (j = MyProc->subxidStatus.count - 1; j >= 0; j--)
|
|
{
|
|
if (TransactionIdEquals(MyProc->subxids.xids[j], anxid))
|
|
{
|
|
MyProc->subxids.xids[j] = MyProc->subxids.xids[MyProc->subxidStatus.count - 1];
|
|
pg_write_barrier();
|
|
mysubxidstat->count--;
|
|
MyProc->subxidStatus.count--;
|
|
break;
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Ordinarily we should have found it, unless the cache has
|
|
* overflowed. However it's also possible for this routine to be
|
|
* invoked multiple times for the same subtransaction, in case of an
|
|
* error during AbortSubTransaction. So instead of Assert, emit a
|
|
* debug warning.
|
|
*/
|
|
if (j < 0 && !MyProc->subxidStatus.overflowed)
|
|
elog(WARNING, "did not find subXID %u in MyProc", anxid);
|
|
}
|
|
|
|
for (j = MyProc->subxidStatus.count - 1; j >= 0; j--)
|
|
{
|
|
if (TransactionIdEquals(MyProc->subxids.xids[j], xid))
|
|
{
|
|
MyProc->subxids.xids[j] = MyProc->subxids.xids[MyProc->subxidStatus.count - 1];
|
|
pg_write_barrier();
|
|
mysubxidstat->count--;
|
|
MyProc->subxidStatus.count--;
|
|
break;
|
|
}
|
|
}
|
|
/* Ordinarily we should have found it, unless the cache has overflowed */
|
|
if (j < 0 && !MyProc->subxidStatus.overflowed)
|
|
elog(WARNING, "did not find subXID %u in MyProc", xid);
|
|
|
|
/* Also advance global latestCompletedXid while holding the lock */
|
|
MaintainLatestCompletedXid(latestXid);
|
|
|
|
/* ... and xactCompletionCount */
|
|
ShmemVariableCache->xactCompletionCount++;
|
|
|
|
LWLockRelease(ProcArrayLock);
|
|
}
|
|
|
|
#ifdef XIDCACHE_DEBUG
|
|
|
|
/*
|
|
* Print stats about effectiveness of XID cache
|
|
*/
|
|
static void
|
|
DisplayXidCache(void)
|
|
{
|
|
fprintf(stderr,
|
|
"XidCache: xmin: %ld, known: %ld, myxact: %ld, latest: %ld, mainxid: %ld, childxid: %ld, knownassigned: %ld, nooflo: %ld, slow: %ld\n",
|
|
xc_by_recent_xmin,
|
|
xc_by_known_xact,
|
|
xc_by_my_xact,
|
|
xc_by_latest_xid,
|
|
xc_by_main_xid,
|
|
xc_by_child_xid,
|
|
xc_by_known_assigned,
|
|
xc_no_overflow,
|
|
xc_slow_answer);
|
|
}
|
|
#endif /* XIDCACHE_DEBUG */
|
|
|
|
/*
|
|
* If rel != NULL, return test state appropriate for relation, otherwise
|
|
* return state usable for all relations. The latter may consider XIDs as
|
|
* not-yet-visible-to-everyone that a state for a specific relation would
|
|
* already consider visible-to-everyone.
|
|
*
|
|
* This needs to be called while a snapshot is active or registered, otherwise
|
|
* there are wraparound and other dangers.
|
|
*
|
|
* See comment for GlobalVisState for details.
|
|
*/
|
|
GlobalVisState *
|
|
GlobalVisTestFor(Relation rel)
|
|
{
|
|
GlobalVisState *state = NULL;
|
|
|
|
/* XXX: we should assert that a snapshot is pushed or registered */
|
|
Assert(RecentXmin);
|
|
|
|
switch (GlobalVisHorizonKindForRel(rel))
|
|
{
|
|
case VISHORIZON_SHARED:
|
|
state = &GlobalVisSharedRels;
|
|
break;
|
|
case VISHORIZON_CATALOG:
|
|
state = &GlobalVisCatalogRels;
|
|
break;
|
|
case VISHORIZON_DATA:
|
|
state = &GlobalVisDataRels;
|
|
break;
|
|
case VISHORIZON_TEMP:
|
|
state = &GlobalVisTempRels;
|
|
break;
|
|
}
|
|
|
|
Assert(FullTransactionIdIsValid(state->definitely_needed) &&
|
|
FullTransactionIdIsValid(state->maybe_needed));
|
|
|
|
return state;
|
|
}
|
|
|
|
/*
|
|
* Return true if it's worth updating the accurate maybe_needed boundary.
|
|
*
|
|
* As it is somewhat expensive to determine xmin horizons, we don't want to
|
|
* repeatedly do so when there is a low likelihood of it being beneficial.
|
|
*
|
|
* The current heuristic is that we update only if RecentXmin has changed
|
|
* since the last update. If the oldest currently running transaction has not
|
|
* finished, it is unlikely that recomputing the horizon would be useful.
|
|
*/
|
|
static bool
|
|
GlobalVisTestShouldUpdate(GlobalVisState *state)
|
|
{
|
|
/* hasn't been updated yet */
|
|
if (!TransactionIdIsValid(ComputeXidHorizonsResultLastXmin))
|
|
return true;
|
|
|
|
/*
|
|
* If the maybe_needed/definitely_needed boundaries are the same, it's
|
|
* unlikely to be beneficial to refresh boundaries.
|
|
*/
|
|
if (FullTransactionIdFollowsOrEquals(state->maybe_needed,
|
|
state->definitely_needed))
|
|
return false;
|
|
|
|
/* does the last snapshot built have a different xmin? */
|
|
return RecentXmin != ComputeXidHorizonsResultLastXmin;
|
|
}
|
|
|
|
static void
|
|
GlobalVisUpdateApply(ComputeXidHorizonsResult *horizons)
|
|
{
|
|
GlobalVisSharedRels.maybe_needed =
|
|
FullXidRelativeTo(horizons->latest_completed,
|
|
horizons->shared_oldest_nonremovable);
|
|
GlobalVisCatalogRels.maybe_needed =
|
|
FullXidRelativeTo(horizons->latest_completed,
|
|
horizons->catalog_oldest_nonremovable);
|
|
GlobalVisDataRels.maybe_needed =
|
|
FullXidRelativeTo(horizons->latest_completed,
|
|
horizons->data_oldest_nonremovable);
|
|
GlobalVisTempRels.maybe_needed =
|
|
FullXidRelativeTo(horizons->latest_completed,
|
|
horizons->temp_oldest_nonremovable);
|
|
|
|
/*
|
|
* In longer running transactions it's possible that transactions we
|
|
* previously needed to treat as running aren't around anymore. So update
|
|
* definitely_needed to not be earlier than maybe_needed.
|
|
*/
|
|
GlobalVisSharedRels.definitely_needed =
|
|
FullTransactionIdNewer(GlobalVisSharedRels.maybe_needed,
|
|
GlobalVisSharedRels.definitely_needed);
|
|
GlobalVisCatalogRels.definitely_needed =
|
|
FullTransactionIdNewer(GlobalVisCatalogRels.maybe_needed,
|
|
GlobalVisCatalogRels.definitely_needed);
|
|
GlobalVisDataRels.definitely_needed =
|
|
FullTransactionIdNewer(GlobalVisDataRels.maybe_needed,
|
|
GlobalVisDataRels.definitely_needed);
|
|
GlobalVisTempRels.definitely_needed = GlobalVisTempRels.maybe_needed;
|
|
|
|
ComputeXidHorizonsResultLastXmin = RecentXmin;
|
|
}
|
|
|
|
/*
|
|
* Update boundaries in GlobalVis{Shared,Catalog, Data}Rels
|
|
* using ComputeXidHorizons().
|
|
*/
|
|
static void
|
|
GlobalVisUpdate(void)
|
|
{
|
|
ComputeXidHorizonsResult horizons;
|
|
|
|
/* updates the horizons as a side-effect */
|
|
ComputeXidHorizons(&horizons);
|
|
}
|
|
|
|
/*
|
|
* Return true if no snapshot still considers fxid to be running.
|
|
*
|
|
* The state passed needs to have been initialized for the relation fxid is
|
|
* from (NULL is also OK), otherwise the result may not be correct.
|
|
*
|
|
* See comment for GlobalVisState for details.
|
|
*/
|
|
bool
|
|
GlobalVisTestIsRemovableFullXid(GlobalVisState *state,
|
|
FullTransactionId fxid)
|
|
{
|
|
/*
|
|
* If fxid is older than maybe_needed bound, it definitely is visible to
|
|
* everyone.
|
|
*/
|
|
if (FullTransactionIdPrecedes(fxid, state->maybe_needed))
|
|
return true;
|
|
|
|
/*
|
|
* If fxid is >= definitely_needed bound, it is very likely to still be
|
|
* considered running.
|
|
*/
|
|
if (FullTransactionIdFollowsOrEquals(fxid, state->definitely_needed))
|
|
return false;
|
|
|
|
/*
|
|
* fxid is between maybe_needed and definitely_needed, i.e. there might or
|
|
* might not exist a snapshot considering fxid running. If it makes sense,
|
|
* update boundaries and recheck.
|
|
*/
|
|
if (GlobalVisTestShouldUpdate(state))
|
|
{
|
|
GlobalVisUpdate();
|
|
|
|
Assert(FullTransactionIdPrecedes(fxid, state->definitely_needed));
|
|
|
|
return FullTransactionIdPrecedes(fxid, state->maybe_needed);
|
|
}
|
|
else
|
|
return false;
|
|
}
|
|
|
|
/*
|
|
* Wrapper around GlobalVisTestIsRemovableFullXid() for 32bit xids.
|
|
*
|
|
* It is crucial that this only gets called for xids from a source that
|
|
* protects against xid wraparounds (e.g. from a table and thus protected by
|
|
* relfrozenxid).
|
|
*/
|
|
bool
|
|
GlobalVisTestIsRemovableXid(GlobalVisState *state, TransactionId xid)
|
|
{
|
|
FullTransactionId fxid;
|
|
|
|
/*
|
|
* Convert 32 bit argument to FullTransactionId. We can do so safely
|
|
* because we know the xid has to, at the very least, be between
|
|
* [oldestXid, nextXid), i.e. within 2 billion of xid. To avoid taking a
|
|
* lock to determine either, we can just compare with
|
|
* state->definitely_needed, which was based on those value at the time
|
|
* the current snapshot was built.
|
|
*/
|
|
fxid = FullXidRelativeTo(state->definitely_needed, xid);
|
|
|
|
return GlobalVisTestIsRemovableFullXid(state, fxid);
|
|
}
|
|
|
|
/*
|
|
* Return FullTransactionId below which all transactions are not considered
|
|
* running anymore.
|
|
*
|
|
* Note: This is less efficient than testing with
|
|
* GlobalVisTestIsRemovableFullXid as it likely requires building an accurate
|
|
* cutoff, even in the case all the XIDs compared with the cutoff are outside
|
|
* [maybe_needed, definitely_needed).
|
|
*/
|
|
FullTransactionId
|
|
GlobalVisTestNonRemovableFullHorizon(GlobalVisState *state)
|
|
{
|
|
/* acquire accurate horizon if not already done */
|
|
if (GlobalVisTestShouldUpdate(state))
|
|
GlobalVisUpdate();
|
|
|
|
return state->maybe_needed;
|
|
}
|
|
|
|
/* Convenience wrapper around GlobalVisTestNonRemovableFullHorizon */
|
|
TransactionId
|
|
GlobalVisTestNonRemovableHorizon(GlobalVisState *state)
|
|
{
|
|
FullTransactionId cutoff;
|
|
|
|
cutoff = GlobalVisTestNonRemovableFullHorizon(state);
|
|
|
|
return XidFromFullTransactionId(cutoff);
|
|
}
|
|
|
|
/*
|
|
* Convenience wrapper around GlobalVisTestFor() and
|
|
* GlobalVisTestIsRemovableFullXid(), see their comments.
|
|
*/
|
|
bool
|
|
GlobalVisCheckRemovableFullXid(Relation rel, FullTransactionId fxid)
|
|
{
|
|
GlobalVisState *state;
|
|
|
|
state = GlobalVisTestFor(rel);
|
|
|
|
return GlobalVisTestIsRemovableFullXid(state, fxid);
|
|
}
|
|
|
|
/*
|
|
* Convenience wrapper around GlobalVisTestFor() and
|
|
* GlobalVisTestIsRemovableXid(), see their comments.
|
|
*/
|
|
bool
|
|
GlobalVisCheckRemovableXid(Relation rel, TransactionId xid)
|
|
{
|
|
GlobalVisState *state;
|
|
|
|
state = GlobalVisTestFor(rel);
|
|
|
|
return GlobalVisTestIsRemovableXid(state, xid);
|
|
}
|
|
|
|
/*
|
|
* Convert a 32 bit transaction id into 64 bit transaction id, by assuming it
|
|
* is within MaxTransactionId / 2 of XidFromFullTransactionId(rel).
|
|
*
|
|
* Be very careful about when to use this function. It can only safely be used
|
|
* when there is a guarantee that xid is within MaxTransactionId / 2 xids of
|
|
* rel. That e.g. can be guaranteed if the caller assures a snapshot is
|
|
* held by the backend and xid is from a table (where vacuum/freezing ensures
|
|
* the xid has to be within that range), or if xid is from the procarray and
|
|
* prevents xid wraparound that way.
|
|
*/
|
|
static inline FullTransactionId
|
|
FullXidRelativeTo(FullTransactionId rel, TransactionId xid)
|
|
{
|
|
TransactionId rel_xid = XidFromFullTransactionId(rel);
|
|
|
|
Assert(TransactionIdIsValid(xid));
|
|
Assert(TransactionIdIsValid(rel_xid));
|
|
|
|
/* not guaranteed to find issues, but likely to catch mistakes */
|
|
AssertTransactionIdInAllowableRange(xid);
|
|
|
|
return FullTransactionIdFromU64(U64FromFullTransactionId(rel)
|
|
+ (int32) (xid - rel_xid));
|
|
}
|
|
|
|
|
|
/* ----------------------------------------------
|
|
* KnownAssignedTransactionIds sub-module
|
|
* ----------------------------------------------
|
|
*/
|
|
|
|
/*
|
|
* In Hot Standby mode, we maintain a list of transactions that are (or were)
|
|
* running on the primary at the current point in WAL. These XIDs must be
|
|
* treated as running by standby transactions, even though they are not in
|
|
* the standby server's PGPROC array.
|
|
*
|
|
* We record all XIDs that we know have been assigned. That includes all the
|
|
* XIDs seen in WAL records, plus all unobserved XIDs that we can deduce have
|
|
* been assigned. We can deduce the existence of unobserved XIDs because we
|
|
* know XIDs are assigned in sequence, with no gaps. The KnownAssignedXids
|
|
* list expands as new XIDs are observed or inferred, and contracts when
|
|
* transaction completion records arrive.
|
|
*
|
|
* During hot standby we do not fret too much about the distinction between
|
|
* top-level XIDs and subtransaction XIDs. We store both together in the
|
|
* KnownAssignedXids list. In backends, this is copied into snapshots in
|
|
* GetSnapshotData(), taking advantage of the fact that XidInMVCCSnapshot()
|
|
* doesn't care about the distinction either. Subtransaction XIDs are
|
|
* effectively treated as top-level XIDs and in the typical case pg_subtrans
|
|
* links are *not* maintained (which does not affect visibility).
|
|
*
|
|
* We have room in KnownAssignedXids and in snapshots to hold maxProcs *
|
|
* (1 + PGPROC_MAX_CACHED_SUBXIDS) XIDs, so every primary transaction must
|
|
* report its subtransaction XIDs in a WAL XLOG_XACT_ASSIGNMENT record at
|
|
* least every PGPROC_MAX_CACHED_SUBXIDS. When we receive one of these
|
|
* records, we mark the subXIDs as children of the top XID in pg_subtrans,
|
|
* and then remove them from KnownAssignedXids. This prevents overflow of
|
|
* KnownAssignedXids and snapshots, at the cost that status checks for these
|
|
* subXIDs will take a slower path through TransactionIdIsInProgress().
|
|
* This means that KnownAssignedXids is not necessarily complete for subXIDs,
|
|
* though it should be complete for top-level XIDs; this is the same situation
|
|
* that holds with respect to the PGPROC entries in normal running.
|
|
*
|
|
* When we throw away subXIDs from KnownAssignedXids, we need to keep track of
|
|
* that, similarly to tracking overflow of a PGPROC's subxids array. We do
|
|
* that by remembering the lastOverflowedXid, ie the last thrown-away subXID.
|
|
* As long as that is within the range of interesting XIDs, we have to assume
|
|
* that subXIDs are missing from snapshots. (Note that subXID overflow occurs
|
|
* on primary when 65th subXID arrives, whereas on standby it occurs when 64th
|
|
* subXID arrives - that is not an error.)
|
|
*
|
|
* Should a backend on primary somehow disappear before it can write an abort
|
|
* record, then we just leave those XIDs in KnownAssignedXids. They actually
|
|
* aborted but we think they were running; the distinction is irrelevant
|
|
* because either way any changes done by the transaction are not visible to
|
|
* backends in the standby. We prune KnownAssignedXids when
|
|
* XLOG_RUNNING_XACTS arrives, to forestall possible overflow of the
|
|
* array due to such dead XIDs.
|
|
*/
|
|
|
|
/*
|
|
* RecordKnownAssignedTransactionIds
|
|
* Record the given XID in KnownAssignedXids, as well as any preceding
|
|
* unobserved XIDs.
|
|
*
|
|
* RecordKnownAssignedTransactionIds() should be run for *every* WAL record
|
|
* associated with a transaction. Must be called for each record after we
|
|
* have executed StartupCLOG() et al, since we must ExtendCLOG() etc..
|
|
*
|
|
* Called during recovery in analogy with and in place of GetNewTransactionId()
|
|
*/
|
|
void
|
|
RecordKnownAssignedTransactionIds(TransactionId xid)
|
|
{
|
|
Assert(standbyState >= STANDBY_INITIALIZED);
|
|
Assert(TransactionIdIsValid(xid));
|
|
Assert(TransactionIdIsValid(latestObservedXid));
|
|
|
|
elog(trace_recovery(DEBUG4), "record known xact %u latestObservedXid %u",
|
|
xid, latestObservedXid);
|
|
|
|
/*
|
|
* When a newly observed xid arrives, it is frequently the case that it is
|
|
* *not* the next xid in sequence. When this occurs, we must treat the
|
|
* intervening xids as running also.
|
|
*/
|
|
if (TransactionIdFollows(xid, latestObservedXid))
|
|
{
|
|
TransactionId next_expected_xid;
|
|
|
|
/*
|
|
* Extend subtrans like we do in GetNewTransactionId() during normal
|
|
* operation using individual extend steps. Note that we do not need
|
|
* to extend clog since its extensions are WAL logged.
|
|
*
|
|
* This part has to be done regardless of standbyState since we
|
|
* immediately start assigning subtransactions to their toplevel
|
|
* transactions.
|
|
*/
|
|
next_expected_xid = latestObservedXid;
|
|
while (TransactionIdPrecedes(next_expected_xid, xid))
|
|
{
|
|
TransactionIdAdvance(next_expected_xid);
|
|
ExtendSUBTRANS(next_expected_xid);
|
|
}
|
|
Assert(next_expected_xid == xid);
|
|
|
|
/*
|
|
* If the KnownAssignedXids machinery isn't up yet, there's nothing
|
|
* more to do since we don't track assigned xids yet.
|
|
*/
|
|
if (standbyState <= STANDBY_INITIALIZED)
|
|
{
|
|
latestObservedXid = xid;
|
|
return;
|
|
}
|
|
|
|
/*
|
|
* Add (latestObservedXid, xid] onto the KnownAssignedXids array.
|
|
*/
|
|
next_expected_xid = latestObservedXid;
|
|
TransactionIdAdvance(next_expected_xid);
|
|
KnownAssignedXidsAdd(next_expected_xid, xid, false);
|
|
|
|
/*
|
|
* Now we can advance latestObservedXid
|
|
*/
|
|
latestObservedXid = xid;
|
|
|
|
/* ShmemVariableCache->nextXid must be beyond any observed xid */
|
|
AdvanceNextFullTransactionIdPastXid(latestObservedXid);
|
|
}
|
|
}
|
|
|
|
/*
|
|
* ExpireTreeKnownAssignedTransactionIds
|
|
* Remove the given XIDs from KnownAssignedXids.
|
|
*
|
|
* Called during recovery in analogy with and in place of ProcArrayEndTransaction()
|
|
*/
|
|
void
|
|
ExpireTreeKnownAssignedTransactionIds(TransactionId xid, int nsubxids,
|
|
TransactionId *subxids, TransactionId max_xid)
|
|
{
|
|
Assert(standbyState >= STANDBY_INITIALIZED);
|
|
|
|
/*
|
|
* Uses same locking as transaction commit
|
|
*/
|
|
LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
|
|
|
|
KnownAssignedXidsRemoveTree(xid, nsubxids, subxids);
|
|
|
|
/* As in ProcArrayEndTransaction, advance latestCompletedXid */
|
|
MaintainLatestCompletedXidRecovery(max_xid);
|
|
|
|
/* ... and xactCompletionCount */
|
|
ShmemVariableCache->xactCompletionCount++;
|
|
|
|
LWLockRelease(ProcArrayLock);
|
|
}
|
|
|
|
/*
|
|
* ExpireAllKnownAssignedTransactionIds
|
|
* Remove all entries in KnownAssignedXids and reset lastOverflowedXid.
|
|
*/
|
|
void
|
|
ExpireAllKnownAssignedTransactionIds(void)
|
|
{
|
|
LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
|
|
KnownAssignedXidsRemovePreceding(InvalidTransactionId);
|
|
|
|
/*
|
|
* Reset lastOverflowedXid. Currently, lastOverflowedXid has no use after
|
|
* the call of this function. But do this for unification with what
|
|
* ExpireOldKnownAssignedTransactionIds() do.
|
|
*/
|
|
procArray->lastOverflowedXid = InvalidTransactionId;
|
|
LWLockRelease(ProcArrayLock);
|
|
}
|
|
|
|
/*
|
|
* ExpireOldKnownAssignedTransactionIds
|
|
* Remove KnownAssignedXids entries preceding the given XID and
|
|
* potentially reset lastOverflowedXid.
|
|
*/
|
|
void
|
|
ExpireOldKnownAssignedTransactionIds(TransactionId xid)
|
|
{
|
|
LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
|
|
|
|
/*
|
|
* Reset lastOverflowedXid if we know all transactions that have been
|
|
* possibly running are being gone. Not doing so could cause an incorrect
|
|
* lastOverflowedXid value, which makes extra snapshots be marked as
|
|
* suboverflowed.
|
|
*/
|
|
if (TransactionIdPrecedes(procArray->lastOverflowedXid, xid))
|
|
procArray->lastOverflowedXid = InvalidTransactionId;
|
|
KnownAssignedXidsRemovePreceding(xid);
|
|
LWLockRelease(ProcArrayLock);
|
|
}
|
|
|
|
/*
|
|
* KnownAssignedTransactionIdsIdleMaintenance
|
|
* Opportunistically do maintenance work when the startup process
|
|
* is about to go idle.
|
|
*/
|
|
void
|
|
KnownAssignedTransactionIdsIdleMaintenance(void)
|
|
{
|
|
KnownAssignedXidsCompress(KAX_STARTUP_PROCESS_IDLE, false);
|
|
}
|
|
|
|
|
|
/*
|
|
* Private module functions to manipulate KnownAssignedXids
|
|
*
|
|
* There are 5 main uses of the KnownAssignedXids data structure:
|
|
*
|
|
* * backends taking snapshots - all valid XIDs need to be copied out
|
|
* * backends seeking to determine presence of a specific XID
|
|
* * startup process adding new known-assigned XIDs
|
|
* * startup process removing specific XIDs as transactions end
|
|
* * startup process pruning array when special WAL records arrive
|
|
*
|
|
* This data structure is known to be a hot spot during Hot Standby, so we
|
|
* go to some lengths to make these operations as efficient and as concurrent
|
|
* as possible.
|
|
*
|
|
* The XIDs are stored in an array in sorted order --- TransactionIdPrecedes
|
|
* order, to be exact --- to allow binary search for specific XIDs. Note:
|
|
* in general TransactionIdPrecedes would not provide a total order, but
|
|
* we know that the entries present at any instant should not extend across
|
|
* a large enough fraction of XID space to wrap around (the primary would
|
|
* shut down for fear of XID wrap long before that happens). So it's OK to
|
|
* use TransactionIdPrecedes as a binary-search comparator.
|
|
*
|
|
* It's cheap to maintain the sortedness during insertions, since new known
|
|
* XIDs are always reported in XID order; we just append them at the right.
|
|
*
|
|
* To keep individual deletions cheap, we need to allow gaps in the array.
|
|
* This is implemented by marking array elements as valid or invalid using
|
|
* the parallel boolean array KnownAssignedXidsValid[]. A deletion is done
|
|
* by setting KnownAssignedXidsValid[i] to false, *without* clearing the
|
|
* XID entry itself. This preserves the property that the XID entries are
|
|
* sorted, so we can do binary searches easily. Periodically we compress
|
|
* out the unused entries; that's much cheaper than having to compress the
|
|
* array immediately on every deletion.
|
|
*
|
|
* The actually valid items in KnownAssignedXids[] and KnownAssignedXidsValid[]
|
|
* are those with indexes tail <= i < head; items outside this subscript range
|
|
* have unspecified contents. When head reaches the end of the array, we
|
|
* force compression of unused entries rather than wrapping around, since
|
|
* allowing wraparound would greatly complicate the search logic. We maintain
|
|
* an explicit tail pointer so that pruning of old XIDs can be done without
|
|
* immediately moving the array contents. In most cases only a small fraction
|
|
* of the array contains valid entries at any instant.
|
|
*
|
|
* Although only the startup process can ever change the KnownAssignedXids
|
|
* data structure, we still need interlocking so that standby backends will
|
|
* not observe invalid intermediate states. The convention is that backends
|
|
* must hold shared ProcArrayLock to examine the array. To remove XIDs from
|
|
* the array, the startup process must hold ProcArrayLock exclusively, for
|
|
* the usual transactional reasons (compare commit/abort of a transaction
|
|
* during normal running). Compressing unused entries out of the array
|
|
* likewise requires exclusive lock. To add XIDs to the array, we just insert
|
|
* them into slots to the right of the head pointer and then advance the head
|
|
* pointer. This wouldn't require any lock at all, except that on machines
|
|
* with weak memory ordering we need to be careful that other processors
|
|
* see the array element changes before they see the head pointer change.
|
|
* We handle this by using a spinlock to protect reads and writes of the
|
|
* head/tail pointers. (We could dispense with the spinlock if we were to
|
|
* create suitable memory access barrier primitives and use those instead.)
|
|
* The spinlock must be taken to read or write the head/tail pointers unless
|
|
* the caller holds ProcArrayLock exclusively.
|
|
*
|
|
* Algorithmic analysis:
|
|
*
|
|
* If we have a maximum of M slots, with N XIDs currently spread across
|
|
* S elements then we have N <= S <= M always.
|
|
*
|
|
* * Adding a new XID is O(1) and needs little locking (unless compression
|
|
* must happen)
|
|
* * Compressing the array is O(S) and requires exclusive lock
|
|
* * Removing an XID is O(logS) and requires exclusive lock
|
|
* * Taking a snapshot is O(S) and requires shared lock
|
|
* * Checking for an XID is O(logS) and requires shared lock
|
|
*
|
|
* In comparison, using a hash table for KnownAssignedXids would mean that
|
|
* taking snapshots would be O(M). If we can maintain S << M then the
|
|
* sorted array technique will deliver significantly faster snapshots.
|
|
* If we try to keep S too small then we will spend too much time compressing,
|
|
* so there is an optimal point for any workload mix. We use a heuristic to
|
|
* decide when to compress the array, though trimming also helps reduce
|
|
* frequency of compressing. The heuristic requires us to track the number of
|
|
* currently valid XIDs in the array (N). Except in special cases, we'll
|
|
* compress when S >= 2N. Bounding S at 2N in turn bounds the time for
|
|
* taking a snapshot to be O(N), which it would have to be anyway.
|
|
*/
|
|
|
|
|
|
/*
|
|
* Compress KnownAssignedXids by shifting valid data down to the start of the
|
|
* array, removing any gaps.
|
|
*
|
|
* A compression step is forced if "reason" is KAX_NO_SPACE, otherwise
|
|
* we do it only if a heuristic indicates it's a good time to do it.
|
|
*
|
|
* Compression requires holding ProcArrayLock in exclusive mode.
|
|
* Caller must pass haveLock = true if it already holds the lock.
|
|
*/
|
|
static void
|
|
KnownAssignedXidsCompress(KAXCompressReason reason, bool haveLock)
|
|
{
|
|
ProcArrayStruct *pArray = procArray;
|
|
int head,
|
|
tail,
|
|
nelements;
|
|
int compress_index;
|
|
int i;
|
|
|
|
/* Counters for compression heuristics */
|
|
static unsigned int transactionEndsCounter;
|
|
static TimestampTz lastCompressTs;
|
|
|
|
/* Tuning constants */
|
|
#define KAX_COMPRESS_FREQUENCY 128 /* in transactions */
|
|
#define KAX_COMPRESS_IDLE_INTERVAL 1000 /* in ms */
|
|
|
|
/*
|
|
* Since only the startup process modifies the head/tail pointers, we
|
|
* don't need a lock to read them here.
|
|
*/
|
|
head = pArray->headKnownAssignedXids;
|
|
tail = pArray->tailKnownAssignedXids;
|
|
nelements = head - tail;
|
|
|
|
/*
|
|
* If we can choose whether to compress, use a heuristic to avoid
|
|
* compressing too often or not often enough. "Compress" here simply
|
|
* means moving the values to the beginning of the array, so it is not as
|
|
* complex or costly as typical data compression algorithms.
|
|
*/
|
|
if (nelements == pArray->numKnownAssignedXids)
|
|
{
|
|
/*
|
|
* When there are no gaps between head and tail, don't bother to
|
|
* compress, except in the KAX_NO_SPACE case where we must compress to
|
|
* create some space after the head.
|
|
*/
|
|
if (reason != KAX_NO_SPACE)
|
|
return;
|
|
}
|
|
else if (reason == KAX_TRANSACTION_END)
|
|
{
|
|
/*
|
|
* Consider compressing only once every so many commits. Frequency
|
|
* determined by benchmarks.
|
|
*/
|
|
if ((transactionEndsCounter++) % KAX_COMPRESS_FREQUENCY != 0)
|
|
return;
|
|
|
|
/*
|
|
* Furthermore, compress only if the used part of the array is less
|
|
* than 50% full (see comments above).
|
|
*/
|
|
if (nelements < 2 * pArray->numKnownAssignedXids)
|
|
return;
|
|
}
|
|
else if (reason == KAX_STARTUP_PROCESS_IDLE)
|
|
{
|
|
/*
|
|
* We're about to go idle for lack of new WAL, so we might as well
|
|
* compress. But not too often, to avoid ProcArray lock contention
|
|
* with readers.
|
|
*/
|
|
if (lastCompressTs != 0)
|
|
{
|
|
TimestampTz compress_after;
|
|
|
|
compress_after = TimestampTzPlusMilliseconds(lastCompressTs,
|
|
KAX_COMPRESS_IDLE_INTERVAL);
|
|
if (GetCurrentTimestamp() < compress_after)
|
|
return;
|
|
}
|
|
}
|
|
|
|
/* Need to compress, so get the lock if we don't have it. */
|
|
if (!haveLock)
|
|
LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
|
|
|
|
/*
|
|
* We compress the array by reading the valid values from tail to head,
|
|
* re-aligning data to 0th element.
|
|
*/
|
|
compress_index = 0;
|
|
for (i = tail; i < head; i++)
|
|
{
|
|
if (KnownAssignedXidsValid[i])
|
|
{
|
|
KnownAssignedXids[compress_index] = KnownAssignedXids[i];
|
|
KnownAssignedXidsValid[compress_index] = true;
|
|
compress_index++;
|
|
}
|
|
}
|
|
Assert(compress_index == pArray->numKnownAssignedXids);
|
|
|
|
pArray->tailKnownAssignedXids = 0;
|
|
pArray->headKnownAssignedXids = compress_index;
|
|
|
|
if (!haveLock)
|
|
LWLockRelease(ProcArrayLock);
|
|
|
|
/* Update timestamp for maintenance. No need to hold lock for this. */
|
|
lastCompressTs = GetCurrentTimestamp();
|
|
}
|
|
|
|
/*
|
|
* Add xids into KnownAssignedXids at the head of the array.
|
|
*
|
|
* xids from from_xid to to_xid, inclusive, are added to the array.
|
|
*
|
|
* If exclusive_lock is true then caller already holds ProcArrayLock in
|
|
* exclusive mode, so we need no extra locking here. Else caller holds no
|
|
* lock, so we need to be sure we maintain sufficient interlocks against
|
|
* concurrent readers. (Only the startup process ever calls this, so no need
|
|
* to worry about concurrent writers.)
|
|
*/
|
|
static void
|
|
KnownAssignedXidsAdd(TransactionId from_xid, TransactionId to_xid,
|
|
bool exclusive_lock)
|
|
{
|
|
ProcArrayStruct *pArray = procArray;
|
|
TransactionId next_xid;
|
|
int head,
|
|
tail;
|
|
int nxids;
|
|
int i;
|
|
|
|
Assert(TransactionIdPrecedesOrEquals(from_xid, to_xid));
|
|
|
|
/*
|
|
* Calculate how many array slots we'll need. Normally this is cheap; in
|
|
* the unusual case where the XIDs cross the wrap point, we do it the hard
|
|
* way.
|
|
*/
|
|
if (to_xid >= from_xid)
|
|
nxids = to_xid - from_xid + 1;
|
|
else
|
|
{
|
|
nxids = 1;
|
|
next_xid = from_xid;
|
|
while (TransactionIdPrecedes(next_xid, to_xid))
|
|
{
|
|
nxids++;
|
|
TransactionIdAdvance(next_xid);
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Since only the startup process modifies the head/tail pointers, we
|
|
* don't need a lock to read them here.
|
|
*/
|
|
head = pArray->headKnownAssignedXids;
|
|
tail = pArray->tailKnownAssignedXids;
|
|
|
|
Assert(head >= 0 && head <= pArray->maxKnownAssignedXids);
|
|
Assert(tail >= 0 && tail < pArray->maxKnownAssignedXids);
|
|
|
|
/*
|
|
* Verify that insertions occur in TransactionId sequence. Note that even
|
|
* if the last existing element is marked invalid, it must still have a
|
|
* correctly sequenced XID value.
|
|
*/
|
|
if (head > tail &&
|
|
TransactionIdFollowsOrEquals(KnownAssignedXids[head - 1], from_xid))
|
|
{
|
|
KnownAssignedXidsDisplay(LOG);
|
|
elog(ERROR, "out-of-order XID insertion in KnownAssignedXids");
|
|
}
|
|
|
|
/*
|
|
* If our xids won't fit in the remaining space, compress out free space
|
|
*/
|
|
if (head + nxids > pArray->maxKnownAssignedXids)
|
|
{
|
|
KnownAssignedXidsCompress(KAX_NO_SPACE, exclusive_lock);
|
|
|
|
head = pArray->headKnownAssignedXids;
|
|
/* note: we no longer care about the tail pointer */
|
|
|
|
/*
|
|
* If it still won't fit then we're out of memory
|
|
*/
|
|
if (head + nxids > pArray->maxKnownAssignedXids)
|
|
elog(ERROR, "too many KnownAssignedXids");
|
|
}
|
|
|
|
/* Now we can insert the xids into the space starting at head */
|
|
next_xid = from_xid;
|
|
for (i = 0; i < nxids; i++)
|
|
{
|
|
KnownAssignedXids[head] = next_xid;
|
|
KnownAssignedXidsValid[head] = true;
|
|
TransactionIdAdvance(next_xid);
|
|
head++;
|
|
}
|
|
|
|
/* Adjust count of number of valid entries */
|
|
pArray->numKnownAssignedXids += nxids;
|
|
|
|
/*
|
|
* Now update the head pointer. We use a spinlock to protect this
|
|
* pointer, not because the update is likely to be non-atomic, but to
|
|
* ensure that other processors see the above array updates before they
|
|
* see the head pointer change.
|
|
*
|
|
* If we're holding ProcArrayLock exclusively, there's no need to take the
|
|
* spinlock.
|
|
*/
|
|
if (exclusive_lock)
|
|
pArray->headKnownAssignedXids = head;
|
|
else
|
|
{
|
|
SpinLockAcquire(&pArray->known_assigned_xids_lck);
|
|
pArray->headKnownAssignedXids = head;
|
|
SpinLockRelease(&pArray->known_assigned_xids_lck);
|
|
}
|
|
}
|
|
|
|
/*
|
|
* KnownAssignedXidsSearch
|
|
*
|
|
* Searches KnownAssignedXids for a specific xid and optionally removes it.
|
|
* Returns true if it was found, false if not.
|
|
*
|
|
* Caller must hold ProcArrayLock in shared or exclusive mode.
|
|
* Exclusive lock must be held for remove = true.
|
|
*/
|
|
static bool
|
|
KnownAssignedXidsSearch(TransactionId xid, bool remove)
|
|
{
|
|
ProcArrayStruct *pArray = procArray;
|
|
int first,
|
|
last;
|
|
int head;
|
|
int tail;
|
|
int result_index = -1;
|
|
|
|
if (remove)
|
|
{
|
|
/* we hold ProcArrayLock exclusively, so no need for spinlock */
|
|
tail = pArray->tailKnownAssignedXids;
|
|
head = pArray->headKnownAssignedXids;
|
|
}
|
|
else
|
|
{
|
|
/* take spinlock to ensure we see up-to-date array contents */
|
|
SpinLockAcquire(&pArray->known_assigned_xids_lck);
|
|
tail = pArray->tailKnownAssignedXids;
|
|
head = pArray->headKnownAssignedXids;
|
|
SpinLockRelease(&pArray->known_assigned_xids_lck);
|
|
}
|
|
|
|
/*
|
|
* Standard binary search. Note we can ignore the KnownAssignedXidsValid
|
|
* array here, since even invalid entries will contain sorted XIDs.
|
|
*/
|
|
first = tail;
|
|
last = head - 1;
|
|
while (first <= last)
|
|
{
|
|
int mid_index;
|
|
TransactionId mid_xid;
|
|
|
|
mid_index = (first + last) / 2;
|
|
mid_xid = KnownAssignedXids[mid_index];
|
|
|
|
if (xid == mid_xid)
|
|
{
|
|
result_index = mid_index;
|
|
break;
|
|
}
|
|
else if (TransactionIdPrecedes(xid, mid_xid))
|
|
last = mid_index - 1;
|
|
else
|
|
first = mid_index + 1;
|
|
}
|
|
|
|
if (result_index < 0)
|
|
return false; /* not in array */
|
|
|
|
if (!KnownAssignedXidsValid[result_index])
|
|
return false; /* in array, but invalid */
|
|
|
|
if (remove)
|
|
{
|
|
KnownAssignedXidsValid[result_index] = false;
|
|
|
|
pArray->numKnownAssignedXids--;
|
|
Assert(pArray->numKnownAssignedXids >= 0);
|
|
|
|
/*
|
|
* If we're removing the tail element then advance tail pointer over
|
|
* any invalid elements. This will speed future searches.
|
|
*/
|
|
if (result_index == tail)
|
|
{
|
|
tail++;
|
|
while (tail < head && !KnownAssignedXidsValid[tail])
|
|
tail++;
|
|
if (tail >= head)
|
|
{
|
|
/* Array is empty, so we can reset both pointers */
|
|
pArray->headKnownAssignedXids = 0;
|
|
pArray->tailKnownAssignedXids = 0;
|
|
}
|
|
else
|
|
{
|
|
pArray->tailKnownAssignedXids = tail;
|
|
}
|
|
}
|
|
}
|
|
|
|
return true;
|
|
}
|
|
|
|
/*
|
|
* Is the specified XID present in KnownAssignedXids[]?
|
|
*
|
|
* Caller must hold ProcArrayLock in shared or exclusive mode.
|
|
*/
|
|
static bool
|
|
KnownAssignedXidExists(TransactionId xid)
|
|
{
|
|
Assert(TransactionIdIsValid(xid));
|
|
|
|
return KnownAssignedXidsSearch(xid, false);
|
|
}
|
|
|
|
/*
|
|
* Remove the specified XID from KnownAssignedXids[].
|
|
*
|
|
* Caller must hold ProcArrayLock in exclusive mode.
|
|
*/
|
|
static void
|
|
KnownAssignedXidsRemove(TransactionId xid)
|
|
{
|
|
Assert(TransactionIdIsValid(xid));
|
|
|
|
elog(trace_recovery(DEBUG4), "remove KnownAssignedXid %u", xid);
|
|
|
|
/*
|
|
* Note: we cannot consider it an error to remove an XID that's not
|
|
* present. We intentionally remove subxact IDs while processing
|
|
* XLOG_XACT_ASSIGNMENT, to avoid array overflow. Then those XIDs will be
|
|
* removed again when the top-level xact commits or aborts.
|
|
*
|
|
* It might be possible to track such XIDs to distinguish this case from
|
|
* actual errors, but it would be complicated and probably not worth it.
|
|
* So, just ignore the search result.
|
|
*/
|
|
(void) KnownAssignedXidsSearch(xid, true);
|
|
}
|
|
|
|
/*
|
|
* KnownAssignedXidsRemoveTree
|
|
* Remove xid (if it's not InvalidTransactionId) and all the subxids.
|
|
*
|
|
* Caller must hold ProcArrayLock in exclusive mode.
|
|
*/
|
|
static void
|
|
KnownAssignedXidsRemoveTree(TransactionId xid, int nsubxids,
|
|
TransactionId *subxids)
|
|
{
|
|
int i;
|
|
|
|
if (TransactionIdIsValid(xid))
|
|
KnownAssignedXidsRemove(xid);
|
|
|
|
for (i = 0; i < nsubxids; i++)
|
|
KnownAssignedXidsRemove(subxids[i]);
|
|
|
|
/* Opportunistically compress the array */
|
|
KnownAssignedXidsCompress(KAX_TRANSACTION_END, true);
|
|
}
|
|
|
|
/*
|
|
* Prune KnownAssignedXids up to, but *not* including xid. If xid is invalid
|
|
* then clear the whole table.
|
|
*
|
|
* Caller must hold ProcArrayLock in exclusive mode.
|
|
*/
|
|
static void
|
|
KnownAssignedXidsRemovePreceding(TransactionId removeXid)
|
|
{
|
|
ProcArrayStruct *pArray = procArray;
|
|
int count = 0;
|
|
int head,
|
|
tail,
|
|
i;
|
|
|
|
if (!TransactionIdIsValid(removeXid))
|
|
{
|
|
elog(trace_recovery(DEBUG4), "removing all KnownAssignedXids");
|
|
pArray->numKnownAssignedXids = 0;
|
|
pArray->headKnownAssignedXids = pArray->tailKnownAssignedXids = 0;
|
|
return;
|
|
}
|
|
|
|
elog(trace_recovery(DEBUG4), "prune KnownAssignedXids to %u", removeXid);
|
|
|
|
/*
|
|
* Mark entries invalid starting at the tail. Since array is sorted, we
|
|
* can stop as soon as we reach an entry >= removeXid.
|
|
*/
|
|
tail = pArray->tailKnownAssignedXids;
|
|
head = pArray->headKnownAssignedXids;
|
|
|
|
for (i = tail; i < head; i++)
|
|
{
|
|
if (KnownAssignedXidsValid[i])
|
|
{
|
|
TransactionId knownXid = KnownAssignedXids[i];
|
|
|
|
if (TransactionIdFollowsOrEquals(knownXid, removeXid))
|
|
break;
|
|
|
|
if (!StandbyTransactionIdIsPrepared(knownXid))
|
|
{
|
|
KnownAssignedXidsValid[i] = false;
|
|
count++;
|
|
}
|
|
}
|
|
}
|
|
|
|
pArray->numKnownAssignedXids -= count;
|
|
Assert(pArray->numKnownAssignedXids >= 0);
|
|
|
|
/*
|
|
* Advance the tail pointer if we've marked the tail item invalid.
|
|
*/
|
|
for (i = tail; i < head; i++)
|
|
{
|
|
if (KnownAssignedXidsValid[i])
|
|
break;
|
|
}
|
|
if (i >= head)
|
|
{
|
|
/* Array is empty, so we can reset both pointers */
|
|
pArray->headKnownAssignedXids = 0;
|
|
pArray->tailKnownAssignedXids = 0;
|
|
}
|
|
else
|
|
{
|
|
pArray->tailKnownAssignedXids = i;
|
|
}
|
|
|
|
/* Opportunistically compress the array */
|
|
KnownAssignedXidsCompress(KAX_PRUNE, true);
|
|
}
|
|
|
|
/*
|
|
* KnownAssignedXidsGet - Get an array of xids by scanning KnownAssignedXids.
|
|
* We filter out anything >= xmax.
|
|
*
|
|
* Returns the number of XIDs stored into xarray[]. Caller is responsible
|
|
* that array is large enough.
|
|
*
|
|
* Caller must hold ProcArrayLock in (at least) shared mode.
|
|
*/
|
|
static int
|
|
KnownAssignedXidsGet(TransactionId *xarray, TransactionId xmax)
|
|
{
|
|
TransactionId xtmp = InvalidTransactionId;
|
|
|
|
return KnownAssignedXidsGetAndSetXmin(xarray, &xtmp, xmax);
|
|
}
|
|
|
|
/*
|
|
* KnownAssignedXidsGetAndSetXmin - as KnownAssignedXidsGet, plus
|
|
* we reduce *xmin to the lowest xid value seen if not already lower.
|
|
*
|
|
* Caller must hold ProcArrayLock in (at least) shared mode.
|
|
*/
|
|
static int
|
|
KnownAssignedXidsGetAndSetXmin(TransactionId *xarray, TransactionId *xmin,
|
|
TransactionId xmax)
|
|
{
|
|
int count = 0;
|
|
int head,
|
|
tail;
|
|
int i;
|
|
|
|
/*
|
|
* Fetch head just once, since it may change while we loop. We can stop
|
|
* once we reach the initially seen head, since we are certain that an xid
|
|
* cannot enter and then leave the array while we hold ProcArrayLock. We
|
|
* might miss newly-added xids, but they should be >= xmax so irrelevant
|
|
* anyway.
|
|
*
|
|
* Must take spinlock to ensure we see up-to-date array contents.
|
|
*/
|
|
SpinLockAcquire(&procArray->known_assigned_xids_lck);
|
|
tail = procArray->tailKnownAssignedXids;
|
|
head = procArray->headKnownAssignedXids;
|
|
SpinLockRelease(&procArray->known_assigned_xids_lck);
|
|
|
|
for (i = tail; i < head; i++)
|
|
{
|
|
/* Skip any gaps in the array */
|
|
if (KnownAssignedXidsValid[i])
|
|
{
|
|
TransactionId knownXid = KnownAssignedXids[i];
|
|
|
|
/*
|
|
* Update xmin if required. Only the first XID need be checked,
|
|
* since the array is sorted.
|
|
*/
|
|
if (count == 0 &&
|
|
TransactionIdPrecedes(knownXid, *xmin))
|
|
*xmin = knownXid;
|
|
|
|
/*
|
|
* Filter out anything >= xmax, again relying on sorted property
|
|
* of array.
|
|
*/
|
|
if (TransactionIdIsValid(xmax) &&
|
|
TransactionIdFollowsOrEquals(knownXid, xmax))
|
|
break;
|
|
|
|
/* Add knownXid into output array */
|
|
xarray[count++] = knownXid;
|
|
}
|
|
}
|
|
|
|
return count;
|
|
}
|
|
|
|
/*
|
|
* Get oldest XID in the KnownAssignedXids array, or InvalidTransactionId
|
|
* if nothing there.
|
|
*/
|
|
static TransactionId
|
|
KnownAssignedXidsGetOldestXmin(void)
|
|
{
|
|
int head,
|
|
tail;
|
|
int i;
|
|
|
|
/*
|
|
* Fetch head just once, since it may change while we loop.
|
|
*/
|
|
SpinLockAcquire(&procArray->known_assigned_xids_lck);
|
|
tail = procArray->tailKnownAssignedXids;
|
|
head = procArray->headKnownAssignedXids;
|
|
SpinLockRelease(&procArray->known_assigned_xids_lck);
|
|
|
|
for (i = tail; i < head; i++)
|
|
{
|
|
/* Skip any gaps in the array */
|
|
if (KnownAssignedXidsValid[i])
|
|
return KnownAssignedXids[i];
|
|
}
|
|
|
|
return InvalidTransactionId;
|
|
}
|
|
|
|
/*
|
|
* Display KnownAssignedXids to provide debug trail
|
|
*
|
|
* Currently this is only called within startup process, so we need no
|
|
* special locking.
|
|
*
|
|
* Note this is pretty expensive, and much of the expense will be incurred
|
|
* even if the elog message will get discarded. It's not currently called
|
|
* in any performance-critical places, however, so no need to be tenser.
|
|
*/
|
|
static void
|
|
KnownAssignedXidsDisplay(int trace_level)
|
|
{
|
|
ProcArrayStruct *pArray = procArray;
|
|
StringInfoData buf;
|
|
int head,
|
|
tail,
|
|
i;
|
|
int nxids = 0;
|
|
|
|
tail = pArray->tailKnownAssignedXids;
|
|
head = pArray->headKnownAssignedXids;
|
|
|
|
initStringInfo(&buf);
|
|
|
|
for (i = tail; i < head; i++)
|
|
{
|
|
if (KnownAssignedXidsValid[i])
|
|
{
|
|
nxids++;
|
|
appendStringInfo(&buf, "[%d]=%u ", i, KnownAssignedXids[i]);
|
|
}
|
|
}
|
|
|
|
elog(trace_level, "%d KnownAssignedXids (num=%d tail=%d head=%d) %s",
|
|
nxids,
|
|
pArray->numKnownAssignedXids,
|
|
pArray->tailKnownAssignedXids,
|
|
pArray->headKnownAssignedXids,
|
|
buf.data);
|
|
|
|
pfree(buf.data);
|
|
}
|
|
|
|
/*
|
|
* KnownAssignedXidsReset
|
|
* Resets KnownAssignedXids to be empty
|
|
*/
|
|
static void
|
|
KnownAssignedXidsReset(void)
|
|
{
|
|
ProcArrayStruct *pArray = procArray;
|
|
|
|
LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
|
|
|
|
pArray->numKnownAssignedXids = 0;
|
|
pArray->tailKnownAssignedXids = 0;
|
|
pArray->headKnownAssignedXids = 0;
|
|
|
|
LWLockRelease(ProcArrayLock);
|
|
}
|